What is a Radiometer?

The radiometer is a light bulb-shaped device containing an object that looks like a weather vane (wings arranged in a circle like spokes of a wheel).  Developed to measure the intensity of radiant energy, or heat, the radiometer will:

1. Help you understand the principles of energy conversion.
2. Show how heat and mechanical energy are products of energy conversion.

Most of us don’t realize how important energy is in our lives.  In actuality, every facet of our life involves energy.  One of the reasons we tend to take energy for granted is that it is constantly changing from one form to another.  We call this change conversion.

During this conversion, energy is changing to and from potential and kinetic forms of energy.  Potential energy is the energy stored in matter; kinetic energy is the energy of motion.  In all energy conversions, the useful energy output is less than the energy input.  This is because some energy is used to do work, and some energy is converted to heat.

Sir William Crookes invented the original radiometer in the mid-nineteenth century.  The device was developed to measure the intensity of radiant energy, or heat.

What causes the vanes of the radiometer to spin?  The atmosphere inside a radiometer is a nearly perfect vacuum.  More than 99% of the air has been removed, leaving only thousands of air molecules inside the radiometer compared to the trillions of air molecules in the outside atmosphere.  The “lighter air” inside the radiometer means that the air molecules are able to move about more freely.

The opposing sides of each vane within the radiometer are alternately dark and light in color.  As light (infrared radiation) hits the vanes, the lighter side reflects the light while the dark side absorbs it.  As the dark side absorbs the radiant energy, a difference in temperature develops between the vanes.  The freely moving air molecules bounce off the dark side with a great deal of energy.  As the air molecules “kick” away from the dark side of the vane, they form convection currents and momentum transfer causing the vanes to spin away from the side from which they kicked (that is away from the dark side of the vane).

Stronger light means that more energy will be absorbed on the dark side, and the air molecules will “kick off” faster and with greater force.  Therefore, as the light gets brighter, the vane begins to spin faster and faster.

Fun Activities to Try With Your Radiometer

Sunlight is responsible or many things, including the production of our food.  Plants use energy from the sun to drive the chemical change in the leaves of plants.  Plants act as an energy converter, and they can change the light energy into chemical energy that plants use to grow.

The following experiments also demonstrate an energy conversation.  This conversion begins with light energy that is changed into mechanical energy and heat.  In all energy conversions, the form of energy changes from a more useful type to a less useful type of energy.  Eventually all of the energy that we use will end up as heat, which is the least useful form of energy.

Always remember to be careful while using your radiometer.  Because it is made of glass, it may break if handled roughly or dropped.  If the radiometer does break, contact an adult immediately to clean the broken pieces.

Experiment #1

What light source works best?

Materials: Flashlight, lamp with an incandescent bulb, mirror

Put you radiometer under different light sources including sunlight.  Which light source makes the radiometer spin the fastest?

Experiment #2

What angle works best?

Hold the radiometer in different positions so light strikes it from different angles.  What angle gives the greatest motion to the vanes?

Experiment #3

Does a mirror increase the intensity?

Use a mirror to add additional light to the radiometer.  Does the mirror make the vanes spin faster or slower?  Why do you think that is?  Try holding the mirror at different angles to add light from different directions.  How does that change the rate of motion?

Experiment #4

Does the radiometer need direct sunlight?

Materials: Flashlight, lamp with an incandescent bulb, mirror, various colors of colored cellophane or colored plastic

Your goal is to find out if the radiometer still spins when the light source has to pass through a colored cellophane or colored plastic.  Use the different light sources from Experiment #3, but place the colored cellophane or plastic between the light source and the radiometer so the light has to pass through it.  Do certain colors allow more light though to make the vanes spin faster?  Do the vanes spin faster or slower with the colored cellophane or the colored plastic?

Experiment #5

The radiometer and heat energy.

Materials: Hair dryer

Use a hair dryer to direct a stream of heat toward the radiometer.  Do the vanes turn at all?  And if so, what happens after a few seconds?  How is this energy source (the hair dryer) different than light energy?

Experiment #6

Will wind affect the radiometer?

Materials: fan or drinking straw

Using the drinking straw or fan, blow air at the radiometer.  Can you get it to turn?  Why or why not?

Experiment #7

Your turn… Can you devise an experiment?

It is your turn to be the scientist.  Now that you know about the radiometer, can you devise an experiment using it? Decide what you’re testing for and test your results!

Educational Innovations sells radiometers for $9.95.

One Pendulum…

Is interesting, but…

Two Pendulums…

Are much more interesting.

But Only If…

They are coupled together.

An Easy Way Is To…

Couple them at their pivot points.  This is accomplished by hanging the two pendulums from a horizontal string.

There Are…

Many illustrations of coupled pendulums on the web; search for ‘coupled pendulums’ – but the fine points of making a really successful demo are rarely discussed… so before we start:

Some Guidelines:

-       Make the pendulums absolutely identical: both the rod lengths and the mass values (the lengths are measured from the pivot points to the C.G. of the masses)

-       Use rod lengths of at least 1/3 meter (13”) – so the pendulums don’t swing too quickly

-       Use masses of at least 75 g (1 oz) – to provide a long swing time

-       Space the vertical supports for a horizontal string length of 500 to 600 mm (20 to 24 in.) – weighted or clamped-down ring stands will work – and will work especially well if their top ends are joined by a solid bar to minimize vibrations

-       The string should be fairly taunt – for example:  a 13 to 15 mm (1/2 to 5/8 in.) droop in the center with two 75 g masses hanging 100 mm (4 in.) apart

-       Use pendulum spacings of 75 to 125 mm (3 to 5 in.) – experiment for good results

-       For the best results, symmetrical setup spacing is critical – try to achieve positions symmetric within 4 mm (1/8 in.)

-       When pulling a pendulum to the side, two things are very important: first, don’t pull it too far (a mass rise of 75 mm (3 in.) is fine); second, the pendulum must be pulled at precisely a right-angle to the string

-       For the following exercises, when two pendulums are raised, they should be raised to the same heights

With Two Identical Pendulums:

Center the two pendulums with the pair spaced about 100 mm (4 in.) apart

-       (A.)  Raise and release one pendulum

Question:  What happens?  Why?

-       (B.)  Raise (on opposite sides) and release both pendulums

Question:  What happens?  Why?

With Three Identical Pendulums:

Center the three with a space of about 75 mm (3 in.) between each

-       (C.)  Raise and release the center pendulum

Question:  What happens?  Why?

-       (D.)  Raise and release one of the outer pendulums

Question:  What happens?  Why?

-       (E.)  Raise (on the same side) and release both outer pendulums

Question:  What happens?  Why?

-       (F.)  Raise (on opposite sides) and release both outer pendulums

Question:  What happens?  Why?

So Far…

We have dealt with identical pendulums… but what happens if we:

-       (G.)  Make a pendulum with a greater mass (but the same length) and use it in place of one of those

above

Question:  What happens?  Why?

-       (H.)  Make a pendulum just slightly longer (say, 20%) than one of the three and use it in place of one of

the pendulums above

Questions:  What happens?  Why?

In Action:

Construction Notes:

-       The horizontal string must be firmly attached (tied, hooked, or taped) to the vertical rods

-       The pendulum rods are made from coat hanger wire or from welding rod

-       Hooks are formed in the pendulum rods using a pair of pliers

-       The masses can be any object that can be affixed to the rod – preferably an object through which a hole can be drilled and, for easy identification during demonstrations, the masses should be different colors

In This Apparatus:

-       Length of horizontal string = 600 mm (23-1/2”)

-       Length of pendulum rods (from inside hook to far end) = 440 mm (17-7/16”)

-       Diameter and material of pendulum rods = 1/8” brass welding rod

-       Thread on end of pendulum rod = 6-32 for a length of ¾ in. (Note 1)

-       Nuts = brass 6-32 knurled (2 per rod)

-       Small mass = 5/8” x 2-1/16” steel rod (75 g) – 3 required (Note 2)

-       Large mass = 1” x 1-3/4” steel rod (175 g) – 1 required (Note 2)

-       Distance from inside of pendulum rod hooks to the centers of masses = 400 mm (15-7/8”)

Note 1:  A No. 6 screw diameter is 0.138”. – the 1/8 in. welding rod is 0.013” less – this is OK

Note 2:  Drilled thru No. 29 (0.136”)

A Comment on Dimensions:

The overall dimensions are not critical, but the apparatus should be large enough to be easily viewed in a classroom setting.

A Definition:

These are ‘Simple Pendulums’ because they are not ‘ideal’: i.e. their masses are not concentrated at single points and the restoring force is not a constant – however they do exhibit ‘Simple Harmonic Motion’.  This motion is an approximation at small angles – it is sufficiently accurate for our purposes.

And Further:

The details of Harmonic Motion and Simple Harmonic Motion are fascinating – the details of both can be found in any physics textbook.

‘Resonance’ is defined as the building up of large vibrations by the repeated application of small impulses whose frequency equals one of the natural frequencies of the body – in this case, a pendulum.  Identical pendulums are required to provide maximum energy transfer.  The mechanical energy is transferred by the ‘pulls’ on the supporting string – this is rather like a child’s swing where ‘pushes’ applied at the correct times will ‘add’ and act to increase the swing amplitude.

In Summary:

These demonstrations provide vivid illustrations of energy transfer between two and three resonant bodies.  Even better, additional pendulums, various masses, and variations of excitation will provide more interesting demonstrations and bases for experimentation.

Marty Sagendorf is a retired physicist and teacher; he is a firm believer in the value of hands-on experiences when learning physics.  He authored the book Physics Demonstration Apparatus.  This amazing book is available from Educational Innovations, Inc. – it includes ideas and construction details for the creation and use of a wide spectrum of awe-inspiring physics demonstrations and laboratory equipment.  Included are 49 detailed sections describing hands-on apparatus illustrating mechanical, electrical, acoustical, thermal, optical, gravitational, and magnetic topics.  This book also includes sections on tips and hints, materials sources, and reproducible labels.

A few months ago I had occasion to conduct two hands-on workshops for elementary and middle school teachers at the NSTA National Convention in San Francisco on behalf of Educational Innovations.  One presentation focused on film canister rockets.  This is a tried-and-true way to teach Newtown’s First and Third Laws of Motion and also brings to light concepts such as the four forces of flight; thrust, drag, weight, and lift.  It also reinforces instruction on 3-D shapes and 2-D plane figures such as circles, cones, cylinders, rectangles, and triangles.

I presented the lesson to the teachers in much the same way I would to my students.  The first thing we did was to brainstorm the features all rockets have.  After a bit of discussion it was agreed that they all have a nose cone, a cylindrical body, fins, and an engine.  I then handed out a paper template imprinted with the pattern of a nose cone and fins, a regular 8½ x 11 sheet of white paper, a piece of goldenrod paper, and a white translucent film canister.  Also required are scissors, tape, ¼ piece of an Alka Seltzer tablet, and paper towels.

The only canister that works with this rocket is the type that has the lid that fits snugly inside the canister.  The canisters that have a lid that wraps around the outside rim, however, will not allow enough pressure to build up inside the chamber.

The first step in building a film canister rocket is to construct the body of the rocket.  The easiest way is to curl the white 8 ½ x 11 paper into a cylindrical shape using the film canister (without the top) as a guide.  The paper can be rolled around the film canister and then taped along the edges.  The easiest way to recover the film canister is to blow into one end of the rolled cylinder, forcing the canister out the other end.

When I conduct this activity I am careful not to offer any suggestion as to whether students should roll the paper in the long or short direction, nor do I discuss how much tape should be used.  The results are very interesting.  Students (adults and children) are very creative, especially when they are not bombarded too much instructional advice.

At this point, you should use Scotch tape to affix the film canister to the cylinder.  This is one of the most critical steps.  First, the canister must have the open end extending far enough from the end of the cylinder so that no tape overlaps the opening of the canister.  If any tape extends over the opening, the lid will not form a complete seal, and sufficient pressure to launch the rocket may not build up.  Second, if the canister is not taped securely, it will launch into the cylinder and propel only the canister rather than the entire rocket.

The next step is to cut out a nose cone and fins.  I use the attached template in my workshops.  The nose cone is actually a circle with a ¼ pie slice cut out.  For those old enough to remember, it closely resembles a Pac Man figure.  The nose cone is made by curling the PacMan so the edges of the missing pie piece begin to overlap forming a cone shape.  Though the template I passed out had cut lines for the nose cone and fins, I give very little direction as to the size of the nose cone or the total number of fins each student should use.

When the construction of the rocket is finally completed, it’s time for the launch!  I have students lay the piece of goldenrod paper on their desk and clear from the launch area any papers or other things that might get wet.  I invite students one at a time to the front of the room so everyone can see the results of their construction techniques.  During teacher workshops where time is limited, I have everyone launch at the same time.

When we’re ready to launch I hand out approximately ¼ piece of an Alka Seltzer tablet.  It is important when working with students to remind them not to put anything in their mouths (especially Alka Seltzer!).  Since the Alka Seltzer is the last step in the process I have students place the tablet piece on the desk and leave it there until I specifically tell them to pick it up!

While holding the rocket upside down students are instructed to fill an eyedropper or pipette with water and add a squirt or two into the film canister.  The amount of water is not critical in the grand scheme of things.

The next step is far more critical, so it is important that students are paying attention at this point.  Once the Alka Seltzer is added to the water in the film canister, it will begin to fizz and give off Carbon Dioxide gas.  The total release of gas is not immediate and therefore will continue for more than a minute which allows plenty of time for the student to secure the cap onto the film canister.  If students become flustered and attempt to jam the top onto their canister while holding the paper cylinder portion of their rocket rather than holding the canister portion they will likely damage their rocket.  Thirty seconds is much longer than most people think.  Having the students relax is the key!  The important thing to remember is to grip the rocket around the film canister and NOT the paper cylinder.

Once the top of the canister is secure the rocket should be placed in the center of the goldenrod paper and the student should step back and wait.  The results are wonderful!!!  Inside the closed film canister pressure continues to build until the container can no longer contain it.  At this point, the top separates from the canister.  Since the top is unable to move with the table behind it, the rocket is propelled upward with a loud popping noise.   Since Goldenrod paper is an indicator for bases, students will notice the launch pattern that is left behind on their launch pad!  Kids find this almost as cool as the rocket launch!

After the activity is over students will note with interest which rockets flew the highest.  This is when the true lesson begins!  Here is the opportunity to identify the many variables and the effects of each variable on the rockets’ flight characteristics.  Examples will include the width of the nose cone, the length of the cylinder, whether any excess paper from the cylinder was trimmed and discarded, and the amount of tape that was added to the rocket during construction.

Since the film canisters are reusable, and the construction materials are quite inexpensive, students should be given the opportunity to redesign their rockets based on discoveries they made during the launch trials and the class discussion.  This is one activity that generates so much enthusiasm with every age group that I fit it in whenever possible.  I’ve brought this activity to Girl Scout meetings with varied ages, Daisys to Cadettes. And with 16 years of teaching experience from 1^st grade to 7^th, I managed a successful launch in each and every class!  This activity is so adaptable that there is certainly no shortage of learning!

On a field trip with my 5^th grade students to a local science museum, we saw one of the science instructors conduct a lesson on sound. It was such a simple idea, with easy-to-find materials, that I brought it home to do with my Girl Scout troop the following week.  Since then, I have modified and expanded the lesson so it would fit any elementary or middle school grade lesson plan on sound.

The first thing students must understand is the simple concept that vibrations create sound.  Even very young children can grasp this concept.  You can conduct a number of activities using tuning forks and such, but the easiest demonstration is to have students touch the front of their throats and hum.  Once they understand that the vibration of the molecules in an object creates sound, they find it easier to understand that sound cannot travel through a vacuum (an area devoid of matter).

The lesson I conducted started off with a single piece of yarn.  Each child was given a 12-inch length and asked to make sound with it.  Generally speaking, very few of my students were successful.  Some realized that, by holding one end of the yarn in one hand, and then running the yarn between the nail of their thumb and pointer finger of the other hand they produced a faint sound.  This was a good beginning!

Next, I gave the students a coffee cup, a paper clip, and a pencil.  I asked them to punch a small hole in the bottom of the cup with the point of the pencil and to thread the yarn through the hole.  They knotted the end of the yarn inside the cup to one end of the paper clip and then pulled the paper clip to the bottom of the cup. The paper clip was flush with the bottom of the cup, and the yarn extended from the bottom of the cup, like an animal’s tail.

While doing this, many students realized that, when they inadvertently ran their hand along the yarn, a sound emanated from the cup.  Without any additional instruction, the children began to experiment on their own.  After a short time, I gave every other student a small cup of water. I instructed them to wet their yarn in the water, without wetting the cup.  As these students ran their hand (or, better yet, their thumb nail) down the yarn it was clear that the sound became significantly louder.

What’s the science behind this activity? The friction between the yarn and students’ fingers caused the yarn to vibrate.  Because there was no way initially to amplify the sound, it remained faint.  As soon as students attached the yarn to the cup, however, the sound became much louder.  This is because the sound waves resonated within the cup and were amplified.  This is the principle at work when children play “telephone,” by stringing two cups across a distance.  The cups amplify the vibrations carried by the string to the listener’s ear.

Similarly, children can change the pitch of the sound by changing the size of their mouth.  This leads to the next step of the lesson.  I distributed aluminum cans of various sizes and had the students attach the yarn to the bottoms of the cans in the same way we did with the cup.  The results should be obvious.  The smaller cans produced a higher pitch while the larger cans produced a deeper and richer sound.

The final activity in my lesson involved Talking Tapes.  These tapes are utilized in much the same way as the yarn in my original lesson. By running their thumb along the plastic strip, students can actually make a paper or plastic cup talk! These tapes are specially molded so that, when vibrated in just the right way, they produce audible speech. And, nothing creates a “buzz” in a classroom like tapes that “talk” to the students!

The principle is the same as a diamond needle traveling through a record groove (if you remember records!).  The Talking Tapes include five assorted phrases and say such things as, “Science is Fun”, “Happy New Year”, and “Be My Valentine”.  Educational Innovations carries Talking Cups and a plethora of other Super! Wow! Neat! materials to teach sound in your classroom!

The normal way to operate a drinking bird is to have him dip his head in water.  The water on his felt head evaporates, leaving the head cooler than the bird’s body.  The liquid flowing into the upper bulb (head) changes the center of gravity, causing the bird to tip forward.  Liquid flows back to the bottom bulb and the bird returns to his upright position.  As long as an adequate temperature difference (head cooler than body) remains, the cycle will repeat.

Instead of cooling the head, why not warm the body?  If you place an electrical resistor below the bird’s body and pass current through the resistor, the resistor will get warm.  The warmth will cause the bird to bob.

I used a 12 ohm, 3 watt resistor and applied 5 volts direct current.  This allows 5/12 amp to flow through the resistor for a total power applied of 2 1/12 watts (P=VI;  5 X 5/12).  The resistor gets hot enough to operate the bird, but not so hot that it melts plastic.

What can you do with this?  I built a clock (actually, I used Peltier cells for the heat, but they are $15. each and they cool slowly, leaving a notable shut off lag).

Binary addition of the bobbing female birds (red) left to right yields the hour.  Binary addition of the bobbing male birds (blue) left to right (multiplied by five) yields the minute (to the nearest five minutes).

Complete instructions and an operating video can be found at: http://www.instructables.com/id/Flock-Clock/

This is a good higher level project that involves math (working in binary), electricity (wiring, relays, transistors, a processor), construction (acrylic, drilling, screws), software (programming the Arduino processor) and art (how you arrange the birds, how you make it look).

It takes about 70 seconds for the bird to start bobbing.  He/she will quit bobbing within 60 seconds after removing power from the resistor.  You can use batteries to power the resistor, but the current load will drain the batteries pretty fast.  If you can obtain an electrical on/off signal, you can make a bird bob on command (with a time delay).  The only limit is your imagination!

Mike Rigsby is a licensed (P.E.) electrical engineer. He writes books and creates projects for children. His latest book, Doable Renewables, Chicago Review Press, Oct. 2009 includes 16 Alternative Energy Projects for Young Scientists.  Chapter three is titled “Solar Drinking Bird.”

You can find the Drinking Bird at Educational Innovations www.teachersource.com.

On a Bright Day:

A great deal of energy falls on the Earth’s surface – roughly 1 kW per square meter.  This is about 0.6 Watt per square inch.  This doesn’t sound like much energy, but suppose we collect and concentrate 63 square inches of this sunlight?  These 63 square inches would collect about 38 Watts of energy.  This doesn’t sound like much, but…

Suppose We Could Then:

Concentrate these 38 Watts into an area of only 1/8 of a square inch?  This is exactly what we can do with an inexpensive plastic Fresnel lens.  We’ll focus the sunlight into an area 3/8” in diameter – this is the equivalent of 300 Watts per square inch!  With this energy level, we can easily ignite a piece of wood, boil some water, and even melt a penny.

A Suitable Device:

Is described in the book, Physics Demonstration Apparatus and in the blog The Sun’s Energy.

Now we’re going to describe how to build a much simpler version that works just as well – one that uses a very inexpensive Fresnel lens and is very easy to construct.

Much Simpler:

In fact, this version so simple and inexpensive that many setups can be made for little more than the cost of the Fresnel lenses.  For each setup:

A lens board:

• A plastic Fresnel lens (7-1/8” x 10-1/4”)
• Two pieces of 11” x 14” corrugated cardboard
• Some masking tape

For the demonstrations shown:

• Four spring-type clothes pins
• A large paper clip
• A penny (minted after 1981)
• A (large-tipped) permanent black marker
• A ½” copper pipe cap
• Detergent
• Water (to fill the pipe cap)

The Lens Construction:

It is absolutely necessary that the Fresnel lens be held ‘plane’ so that it may achieve a good focus.  To achieve this, two pieces of corrugated cardboard are used to mount the lens – their corrugations are placed at right angles.

• Ensuring that the hole outline in each piece is correctly oriented, cut an opening in each which is ½” smaller than the lens – use a single-edge razor blade or a hobby knife.  When laminated, this pair will be much stiffer (and planer) than a single piece of cardboard or two pieces with parallel corrugations.
• Place the two cardboard pieces together and, using masking tape, tape the hole edges and the outer edges together
• Place the lens over the opening and tape it over the opening with the grooved face downward (to protect the face from scratches)
• A NOTE:  It’s a strange property of corrugated cardboard: it always seems to warp – to counteract this I store these lenses under some heavy books

Of Absorbance:

The ‘blacker’ the absorbing surface – the greater the amount of energy absorbed.

Of Thermal Conductivity:

For our purposes, less is better – the object to be heated should be supported such that there is minimal energy loss via the supporting device – hence the use of ‘low-contact-area’ paperclips for holding a penny or a piece of wood supporting a pipe cap.

Igniting Wood:

It really isn’t necessary to make a black spot on wood – it will quickly ignite.  For even faster ignition, use a black marker to make a 3/8” diameter ‘spot’ at the focus location.

A Simple ‘Water Holder’:

We’ll use a ½” copper pipe cap (sometimes called a ‘tube cap’).  However, because the copper is highly reflective, we need to make its surface much darker – the darker the better.

Clean the pipe cap with strong detergent (to remove any residual oil).  Dry it well.  Use the black marker to ‘color’ both the inside and outside surfaces.

Remember to mention to the students that so long as the pipe cap contains water, its temperature cannot exceed the boiling point of water.  But, if the water is boiled off, the cap’s temperature will rise to that which the concentrated sunlight can produce – allowing this to occur may ‘burn’ the cap’s coating – to reuse the cap simply blacken it again.

A Simple ‘Penny Holder’:

Using the black marker, make a (very black) ‘spot’ about 3/8” in diameter in the center of the penny’s face.  Bend (using pliers) the paperclip as shown – note the small ‘hook’ at the end of the inner part of the paperclip, this prevents the penny from ‘squeezing’ out.

In Use:

Good results require a bright & clear sky – even a slight haze will dramatically decrease the sun’s available energy.  Interestingly enough, even the sunlight on a very clear day in the winter will provide sufficient energy for good demonstrations – however, the noonday ‘higher sun’ in the summer months is far better.

Place the object to be heated on the ground.  Two students holding opposite sides of the lens board can position the board for direction and focus.  The ‘altitude’ of the sun will determine the positioning (height and angle) of the lens and the positioning of the object to be heated.  A support for the bottom edge of the lens board will enhance stability (e.g. a box or a stack of books).  It is necessary to focus and maintain the focus for a continuous period (sometimes up to 60 seconds) to achieve the necessary heating time.

The lens must be orientated perpendicular to the sun’s rays, with the object to be heated located directly in-line behind the lens.  A typical Fresnel lens of this type has a focal length of 10” to 11”.  The ‘ruled’ side of the lens must face the sun.

Some Examples:

Focus the sunlight into the smallest spot possible (1/4” – 3/8” dia.).

The sunlight need only be focused such that the whole spot area is smaller than the black surfaces of pipe cap.

Construct the ‘penny holder’ such that the penny is held perpendicular to the light beam.  Focus the sunlight into the smallest spot possible (1/4” – 3/8” dia.).

Some Obvious Cautions:

This lens will produce temperatures in excess of 600 degrees F (300 degrees C)!  Caution students that they must not place their hands (or anything else) within the concentrated sunlight.  It is highly recommended that everyone wear (U-V resistant) sunglasses if they are likely to look directly at the object being irradiated (there can be a great deal of reflected U-V energy).   Advise students not to handle any object that has been heated until it is cooled sufficiently.  For a penny, this can take several minutes.

NEVER LOOK AT THE SUN THROUGH THE LENS ! ! !

These Are:

Great demonstrations for any General Science, Earth Science, Physical Science, or Physics class.  They truly do illustrate the energy in everyday sunlight – energy that we all know is ever-present, but little appreciate its magnitude until we actually witness its concentrated power.  Or:

Truly memorable Solar Energy Labs can be created wherein each group of students is supplied with:

• A lens board (pre-made)
• Several clothespins
• Several paperclips
• A piece of wood (like, 4” x 4” square)
• A ½” copper pipe cap (previously cleaned)
• A U. S. penny (1982 or after)
• A large-tipped permanent black marker
• A few mL of water
• A pair of pliers (for bending paperclips)
• Sunglasses or darkened glass/plastic (U-V rated)

The assignments:

1. Discover how quickly how some materials – like wood – can be quickly ignited (time required?)
2. Construct a support for a penny and melt a penny (time required?)
3. Boil a small quantity of water (time required?)

Some follow-up questions:

• “Why does the wood ignite so quickly?”
• “Why does it take a longer time for the penny to melt (than for the wood to ignite)?”
• “Why does the water boil so quickly?”
• “Why is it (sometimes) necessary to have a black surface on the material to be heated by the sunlight?”

A Pre-Lab:

Might include discussions about:

• Energy (the ability to do work)
• Solar energy
• Energy conversions (light to thermal)
• Absorption/Reflectance
• Specific Heat
• Lenses (common and Fresnel)

And possibly:

• Each group constructs their own lens board

Notes:

• Remember, the actual exercises must be done on a day when the sunlight is ‘really bright’ – anything less simply will not provide the energy necessary.
• Always store a Fresnel lens away from direct sunlight – under the correct circumstances it can start a fire.
• ‘Dusting-off’ the Fresnel must be done with compressed air – wiping with paper or cloth will scrape material into the grooves and diminish its optical quality.

Guidelines for building the Atomic Penny Vaporizer are detailed in the book Physics Demonstration Apparatus.  This amazing book is available through Educational Innovations and includes ideas and construction details, including all equipment necessary, for the creation and use of a wide spectrum of awe inspiring physics demonstrations and laboratory equipment.  Included are 48 detailed sections describing hands-on apparatus illustrating mechanical, electrical, acoustical, thermal, optical, gravitational, and magnetic topics.  This book also includes sections on tips and hints, materials sources, and reproducible labels.

When two 1-pound, 2-inch diameter, chrome steel spheres are smashed together, enough heat is generated at the point of contact to burn a hole in ordinary paper!  This dramatic demonstration has been a favorite of students in every grade for as long as I have been teaching!

There are a few considerations when allowing students (especially younger ones) to conduct this activity on their own…  First, the spheres are pretty heavy, so if they were either dropped on a foot or onto a nice tile floor, the result would not be good.  Also, be sure that the only thing between the spheres is paper or aluminum foil.  Fingers caught between the colliding spheres would not  be happy.  Finally, all participants should wear safety glasses, as it is not unusual for a small piece of paper to fly off after the spheres collide.

The Procedure:

Have an assistant hold the top edge of a piece of regular white paper vertically.  Hold one sphere in each hand on either side of the paper.  Quickly move the spheres together until they collide against the paper.  If they do not burn a hole in the paper the first time, try again and move the spheres together more quickly.  Examine the hole in the paper.  You will see that the areas around the edges of the hole are actually singed, and you will smell the burning paper!

Repeat the activity; however, this time use aluminum foil in place of the paper.  You will observe concentric circles radiating outward from the impact point.  This is a clear way to visualize shock waves!

Explanation:

This demonstration graphically illustrates how kinetic energy is transformed to heat energy.  Though some sound energy is produced, the force centered at the small where the spheres collide generates enough heat energy to burn the paper.  According to Newton, F=MA.  The amount of force between the two spheres is a function of the mass (which is constant) and the acceleration (which is controlled by the person moving the steel spheres).  The faster one smashes the spheres together, the greater the force.

A note from Ron Perkins:

Some time around 1996, the Smashing Steel Spheres demonstration was presented to a group of teachers in Dr. Larry Peck’s, AP summer program at Texas A&M, taught by Kristen Jones and Lisa McCaw.  One enterprising teacher tried the demonstration later that evening with some old spheres that he had around the house.  Imagine his surprise when he obtained sparks after colliding the rusty spheres together with a piece of aluminum foil held in between.  He had rediscovered the thermite reaction: Fe3O4+Al ->Fe+Al2O3+Heat and Sparks. (the numbers in the equation should be subscript, but there is no way to do this in the program we use for the blog…)

Since then, there has been a frantic search for rusty spheres.  It is possible to rust the Educational Innovations’ spheres, but it is usually a very slow process.  Dr. David Shaw, MATC in Madison, Wisconsin, has reported that a few months in the presence of fumes from the chemical storage closet works well…

It never fails.  I get the same reaction, whether I present to seasoned physicists, grade level science teachers or even from the most discerning audience I’ve had; a group of fifty – fourth grade students, jaws gape and sounds of oohs, aahs and wows issue forth.

I’ve been in rooms surrounded by hundreds of artificial light sources, from the simplest incandescent bulbs to the most advanced OLED displays, and even so, when a person closes that knife switch and current begins to flow and a simple piece of pencil lead held suspended inside a partially evacuated chamber starts to glow brighter, brighter, and finally white light illuminates the chamber, something happens in the person’s brain.  At once they are connected with the wonders that Sir Humphry Davy, Swan, and Edison felt when they experimented with the world’s first electrical light sources.  Questions start to form; How does that work? How could we make it last longer? What would happen if we changed the carbon for some other material?  All at once, the passive viewer is thinking scientifically, asking questions, and yearning to do more.

I’m talking about “Reinventing Edison: Build your own Light Bulb”, a science kit that I am proud to have designed.  I created the kit to be fun and interesting while at the same time integrating history and invention into science and mathematics.  The kit is designed to work as a safe, hands-on, inquiry based science experiment for both qualitative and quantitative experiments.  But It also works well as an engaging  demonstration at the front of the classroom.

Some ideas for demonstrations include:

1)    As an example of science, invention, and history for your grade 3-5 class.

2)    As a day one introduction to your middle school physical science class.

3)    As an introduction to your high school physics class or electricity lessons.

4)    As a demonstration of quantitative data gathering and properties of matter for your middle or high school physical science class.

5)    As an illustration of the scientific method AND proper safety procedures for your technology or engineering class.

6)    As a demonstration to introduce the electricity section of your college physics lecture.

No matter what your grade level or subject area, the Reinventing Edison kit can be a very effective way to create interest in your students, get them asking questions, and help them to get excited about what will come next in your science lectures or labs.

This article will detail some tips and tricks for effectively using the kit as a demonstration based upon my own experience using the kit in front of many different audiences.  I will not go into specific details on how to setup or use the kit as those instructions are included in the instruction and experiment manual that is included with the kit.

First things First: Safety

The Reinventing Edison kit is designed with safety in mind, however as with any science experiment or demonstration there is some risk involved if proper safety procedures are not observed.  Make sure to read, understand, and follow all safety instructions printed in the manual.  Risk of eye injury is minimal, but it is always a good idea to wear eye protection both for your safety and to demonstrate proper lab procedures.

Filaments, especially the carbon and tungsten filaments, will glow to incandescence, potentially emitting a bright white light that can light up a room.  It’s advised that you and your audience never stare directly at the filament after it starts to glow beyond a cherry red color.

Remember filaments and conductors of heat in contact with the filaments will get very hot.  Always allow a minute or more for the filament, clamps, and bulb cap to cool before handling after each experiment.  In this way you will avoid singed finger tips and can avoid uttering things that you shouldn’t in front of sensitive ears (such as the seasoned physicists that I mentioned above).

Always wear a lab coat while performing experiments with the Reinventing Edison kit.  This is in no way a safety issue, they just look cool…

Keep Things Simple

In some of my first demonstrations of the Reinventing Edison kit I made the mistake of trying to cram too much into a short period of time and performed in front of a large audience.  I had volt and current meters set up, multiple power sources, and was prepared to talk for hours about the history of Edison. I forgot my purpose was simply to grab the attention of my audience and not to teach a years worth of electrical engineering and history!  The important lesson that less is more had eluded me.

When using the Edison kit as a demonstration I recommend that you choose a simple configuration (series circuit) with a filament choice that will give a guaranteed result the first time you throw the switch.  The included carbon filament (pencil lead) works best, glows red for a time, and then glows bright white for a minute or more before burning out.

The included tungsten filament glows bright white for a lot longer than the carbon filament, and as a result, might actually have less of an impact than a filament that burns out within a minute or so.  An audience of any age will have their wow moment as soon as the filament reaches incandescence and will usually sit spell bound for about a minute wondering if it will burn out (especially if you keep them going with what you are saying), but they won’t usually last for the three or more minutes that a tungsten filament may last for.  Save the Tungsten filament as a closing experiment and give a quick lecture or answer questions while you wait for it to burn out.

Remember the History!

Reinventing Edison is as much about history and invention as it is about science or math.  I like to start any demonstration by asking the audience to close their eyes and imagine a time when there was no light source except the sun or fire.  When it was dangerous or impossible to travel at night time.  When a forgotten candle might burn down your house.  When you didn’t have electrical devices in your home because you didn’t have electricity in your home.

I then talk about Edison and how creating the light bulb was not solely his achievement.  It’s good to talk about earlier demonstrations that  Sir Humphry Davy performed using giant batteries and carbon filaments for college audiences as well as the contributions of the English chemist Swan.  Edison patented the bulb and all of the systems required to manufacture, distribute, and power them first, but even then, it was not solely his effort.  He had a team of hundreds working for him.

The following link contains a bibliography of sources that I used to research the science and history behind Edison and the Light Bulb.  If you want to learn more I highly recommend the sources listed.

http://www.scribd.com/doc/18219124/Reinventing-Edison-Reading-List

Be Prepared – BUT remember, when things go wrong this is a teachable moment!

Its a good idea to perform your intended experiment by yourself before you have an audience in order to work out any bugs, determine the timing requirements, and learn how to deal with any “surprises” that you may experience.  I’ve found that mistakes or problems while operating the bulb often work to build suspense in an audience and function as “teachable moments” to illustrate science facts.  If you do encounter problems, remind your students that Edison experimented for several years with thousands of different filament materials until he got a bulb to work!

When I demonstrated the bulb to a group of 50 fourth grade students I had wired my batteries incorrectly.  So I talked about the bulb, how it worked, what I was going to do next.  I asked my assistant to dim the lights and then to flip the switch.  And when they did, the filament smoked and immediately exploded into two pieces.  Too much current, too little voltage, no incandescence.  I still got a wow when it exploded (thanks to the camera projecting the bulb onto a larger screen) but not the BIG wow I wanted from the moment of incandescence itself.  Without missing a beat I talked about Edison’s thousands of experiments and asked the audience if they thought two or three tries for us would still be respectable.  I then talked about the problem (parallel batteries instead of series batteries) and told them I would wire the circuit a different way, changing a variable, and seeing what would happen next.  My blunder turned into a “I meant to do that” moment that would have made professor Pee Wee proud.

Get The Audience Involved and Have Fun!

The more interactive your presentation is the better it will be.  Everyone has sat in boring power point slide lectures that left them less intelligent than when they came into the room, and most of us have ended up giving a few of those presentations in our careers, too.  But remember, science is about asking questions.  Ask your audience (the students) questions about what you are doing.  Who invented the light bulb (they’ll say Edison, you can counter with “he is credited with inventing it, but have you heard of Swan?”)  Ask them to predict what will happen next if you change something about your experiment.  Ask for volunteers to verify that the pencil lead you are putting into the bulb is really just ordinary pencil lead.  Get a volunteer to throw the switch or ask the crowd to countdown like a rocket launch.  Most importantly have fun with what you are doing.  You are modeling the idea that science and technology can be interesting and rewarding not just math-filled, difficult, or boring.  If something goes wrong, use it as a moment for comedy.  I had an electronics teacher in high school who every year would work on a TV set during open lab periods and every year he’d cause a huge electrical arc to jump between the high voltage terminal and the chassis seemingly by accident.  He’d then jump up and run away from the bench in fear in a display that would have made Lou Costello proud.  This definitely got students attention and made for a memory that I still have decades later.  Just remember, keep things serious around safety and around facts, but keep things fun, open, and accessible overall.

Don’t forget the vacuum

Your demonstration is likely focused on electricity and light, and hopefully history, but it’s easy to forget what isn’t there… the vacuum!  Achieving incandescence in a filament is dependent upon removing as much air from the bulb as possible.  Air hinders incandescence in three ways; air conducts heat away from the filament such that it does not heat up to the point of incandescence, air can support combustion of materials like carbon and thus causes them to physically burn up quickly, and the oxygen in air can combine with the hot filament material and oxidize it weakening its structure and causing it to burn out more quickly.

Obviously the hand vacuum pump included in the kit cannot remove all of the air in the bulb, but it does remove enough that you can achieve several minutes of operation from carbon and tungsten filaments.  Air is invisible, and so to illustrate the working of the pump you can ask for a volunteer to report their observations. For example, hearing the pump operate, feeling as it becomes harder to move the piston as they remove more air, and feeling for the air that is coming out of the pump.  You can also use the bulb (minus a filament and electrical connections) as a mini-bell jar and use it to boil a small amount of water, inflate a small tied balloon, or expand a marshmallow.

An interesting fact: Many years ago, light bulbs had a nearly complete vacuum, so if they broke they made a very deep implosion sound (check out any black and white film where a light bulb breaks to hear what this sounded like).  Today bulbs are only evacuated to about one fourth atmospheric pressure with the oxygen replaced by the inert gas Argon.

Due to risk of implosion I don’t recommend that you try to use a powered vacuum pump with this kit.

Finally a few technical tips for a good demonstration

We’ve received very few trouble reports from users of the kits since we started making them in 2004, but we have found that 99.9% of all problems have come from using the wrong kind of power supply.  For best results make sure you use two fresh 6-volt Alkaline lantern batteries.  Carbon Zinc batteries are less expensive, but they cannot supply enough current to support incandescence.  Alkaline batteries almost always say “Alkaline” but Carbon Zinc batteries usually just say “Battery”… one way to tell the difference is that most Alkaline batteries have a metal shell and Carbon Zinc batteries have a plastic or even cardboard shell.  Also, make sure you keep up with the cap-covers for the batteries. Cap-covers are plastic insulators that prevent the metal terminals on the battery from shorting out if they come into contact with a conductor.

The top stopper in the kit is designed to pull inside the clear plastic tube should an actual vacuum pump be used with the kit.  This is an intentional design put in place to to avoid any implosion risk.  Since rubber stoppers vary a little bit in diameter and are softer when they are new, your top stopper might pull inside the tube when you use the hand-vacuum pump.  If this happens you can fix the problem by tightening the hex-nuts on the screws that pass through the stopper.  You should also make sure to press the vacuum release stopper as deeply as possible into its port.  This will cause the stopper to expand in diameter a little bit and should reduce its tendency to pull inside the tube.  If the stopper does pull inside the tube, you can retrieve it most easily by removing all wiring and the vacuum pump and then push the stopper through from the top to the bottom of the tube.  This is another reason to assemble and test your kit before going on stage in front of an audience.

Always remember to open the knife switch on the bulb after every experiment.  When the filament burns out it is very easy to immediately jump to changing the filament for your next experiment.  Remember, if you don’t open the switch then you can potentially cause a short circuit while handling the bulb cap, or you may have a hot filament in open air or in your hands while you work with it.  Always double check the knife switch before changing the filament!

For a High School or College level demonstration of the kit, it can be useful to monitor, display, or report the voltage drop across the filament and current drawn by the filament.  This can easily be accomplished by standard bench meters, display meters, or even probeware or data logging equipment.  It is important to make sure that you use equipment rated for the voltage source you are using (usually 10 volts since you will be using 6 volts, and 1-amp or higher for current).  Light levels may also be monitored and compared to voltage/current using data logging or probeware equipment.

For Frequently Asked Questions and Troubleshooting tips you can read or download the following document: http://www.scribd.com/doc/18400229/Reinventing-Edison-FAQ-and-Troubleshooting

Conclusion

Thank you for reading this article.  I hope that you found it interesting and learned at least one or two things that will help you make a spectacular presentation to your students.  Enthusiasm for all areas of STEM education is important, and if we can help inspire just one person all of our efforts were worthwhile.

If you use the Reinventing Edison: Build your own Light Bulb kit in your class, for a demonstration or as a classroom activity we’d love to have your feedback.  Feel free to share pictures, video clips, or comments with us at our Fan Page on Facebook: http://www.facebook.com/HarrisEducational.

About the Author

Bennett M. Harris holds a degree in Technology Education from North Carolina State University and has many years of experience developing educational materials, teaching, and tutoring students of all ages in many different STEM (Science, Technology, Engineering, and Mathematics) topics.  Bennett is the founder of Harris Educational and the originator of Reinventing Science kits.

Imagine students’ amazement when they actually see sunlight melt a penny!  This demonstration clearly illustrates the vast amount of energy illuminating the Earth’s surface.  In rough numbers: 70% of the Sun’s incident energy on our outer atmosphere is reflected back into space – only about 30% actually gets to the Earth’s surface.  But, as we experience, this is still a substantial quantity of energy.

Fortunately, this energy (I. R. – Visible – U. V.) is rather uniformly distributed over the Earth’s surface -  thus its overall intensity is such that we have a habitable environment.  However, as we all know, we can concentrate some ‘area’ of this energy to increase the ‘energy per area’ (a measure of this is the temperature of the area of concentrated energy).  A common magnifying lens (2-4 in. diameter) will concentrate sufficient energy to burn paper or other objects with a low flash point.

To achieve an even higher energy concentration it is only necessary to use a device that increases the ‘capture area’ of the Sun’s energy.  Fortunately, this is easily accomplished with an inexpensive ($3.50) Fresnel lens.  The Fresnel lens (64 sq. in.) used here will ‘collect’ nine times the energy of a 3 in. diameter magnifying lens –creating a ¼” diameter ‘spot’ of energy having a temperature of over 315 degrees C (600 degrees F).  This is sufficient energy to melt zinc.

All that’s required are a Fresnel lens, bright sunlight, and a means of holding a penny.  Actually, it is a bit more involved: the Fresnel lens must be positioned exactly perpendicular to both the sunlight and the penny; the penny must be of 1982 or later; and the penny must be supported by a thermally minimally-conductive means.

Guidelines for building the Atomic Penny Vaporizer are detailed in the book Physics Demonstration Apparatus.  This amazing book is available through Educational Innovations and includes ideas and construction details, including all equipment necessary, for the creation and use of a wide spectrum of awe inspiring physics demonstrations and laboratory equipment.  Included are 48 detailed sections describing hands-on apparatus illustrating mechanical, electrical, acoustical, thermal, optical, gravitational, and magnetic topics.  This book also includes sections on tips and hints, materials sources, and reproducible labels.

And, as a footnote, it is not illegal to ‘vaporize’ a penny or any other United States currency.  By law, it is only illegal to alter U. S. currency if the intent is to defraud – melting a penny with the Sun’s energy is simply a wonderful example of energy and its effects – perfectly legal.

This uniquely entertaining ball is a fun way to demonstrate open and closed circuits, as well for prompting discussions on conductivity. The following activities are perfect to use in elementary and middle school grades first exploring electricity and circuits.

When both sensors on the ball are touched and a complete circuit is formed, the ball flashes a red light and buzzes.

What makes the energy ball work?

Inside the energy ball is a simple circuit that is completely self-contained. By touching both sensors, the circuit is completed by electrons flowing through your body or another conductive material such as a paper clip. Materials that activate the energy ball are good conductors, meaning they pass electrons easily. Materials that do not activate the energy ball are poor conductors (or insulators), meaning they do not pass electrons easily. Your students will enjoy finding different ways to activate the ball:

One Student: Simply hold the ball so that both sensors are touched or, press one sensor with your hand and the other with a paperclip. Try experimenting with other materials (cardboard, plastic, metal) to see which will activate the ball.

Multiple Students: Using two students, have each student touch a sensor, and then hold hands with one another. See how many students can hold hands and still keep the energy ball buzzing. This is an easy way to demonstrate the difference between open and closed circuits – designate one student to be the “switch.” If the switch releases one or both of the hands they’re holding, the ball will stop flashing, representing an open circuit. Holding hands again will resume flashing, and the circuit will be closed.

An Entire Class: For a fun teaching game, try playing a variation of “Duck, Duck, Goose,” with the energy ball. First, form a circle of hands with the energy ball between two students.  One student should be outside the circle, who will be “it.” This student should then go around the circle, pointing to each person in turn and saying either “closed” or “open.” Once a person has been designated “open,” he or she should break the circuit and try to make it around the circle and complete the circuit before the person who was “it”.

Educational Innovations sells the Energy Ball (SS-30) for $3.95.