A. Forces
1. Use one of the new scales which is marked in newtons, to give the students a feel for newtons.
2. Center of mass: use several cutouts, including one with the center of mass outside the body. Show the figure with weights held below the feet, on a bent rod, that will balance even when hit.

B. Motion
1. Hunter and monkey: an air cannon shoots a monkey released by a magnet when the cannon fires, and both the monkey and bullet are falling.
2. Air track: use a timer to demonstrate constant velocity with a cart on an air track (Newton's first law). Put a book under one end to demonstrate acceleration (Newton's second law).
3. F= ma. Use the cast iron track with 1-kg car pulled by a pulley with 50-g mass (1/2 N) to show acceleration. Then double the car mass with a 1-kg mass and repeat. Remove the extra mass and double the pulling mass with a 50-g attachment, and repeat. Finish off by doubling both the car mass and pulling mass and compare to the original acceleration. This is all without measurements, but is visually effective.
4. Trajectory of center of mass: get two balls, one normal and one weighted off center, and toss through the air.
5. Radial acceleration: twirl a small mass on a string above your head, with a newton scale between your fingers and the string. You can't read the scale while in motion, but you can tell when it bottoms out at a high enough speed, and in any case the class gets the idea that a higher speeds pulls harder on the string.

C. Energy
1. A pendulum is nice for explaining the continual trade-off between KE and PE, with constant total energy. The bowling ball pendulum is best, but is more trouble to hang.
2. Work:
a. Use a newton scale to pull a block along the lecture table, beside a meter stick, and calculate the word done.
b. Use a newton scale to lift a l-kg mass vertically beside a meter stick, and calculate the work done.
c. Use a newton scale to accelerate an object (on wheels, little friction) and calculate the work.
In each case above, point out where the energy ended up: (a) heat, (b) PE, and (c) KE.

D. Gravity
1. Gallileo's experiment: Stand up on the lecture table and drop balls of different mass; the lead and wooden balls are best because the masses are so different, and if the acceleration did depend on mass one would expect an obvious difference in the fall times. Repeat several times, perhaps with different balls.
2. Measure g by dropping a steel ball from the ceiling. Stand on the lecture table and hold the ball at the ceiling. Have one student count down to zero, and at that point one student will start a stopwatch and another student will start the large times that came with the large airtrack, and you will drop the ball. The students will stop their timers when they hear the ball hit the floor. The fall time is under one second, so the result will be crude, but it is worthwhile carrying out this most direct method of measuring g so the students can appreciate the large size of g and so that you can discuss errors, preparing for the next item below.
3. Measure g by three other methods.
a. Since the problem with the direct method above is the short fall time, use an inclined plane to effectively reduce g and thus lengthen t. The long air track is ideal for this, with the large timer.
b. Even with small fall times, a repetitive technique would allow one to integrate data. Use a source of water drops that produces drops at the rate of about one per half-second. (A large hypodermic needle and syringe works well.) Stand on the lecture table and let the drops fall on a piece of paper on the floor, so that you can hear the drops hit, and raise the source higher and higher until you see a drop leave the source precisely as you hear the previous drop hit the paper. Then, by counting perhaps 30 drops and measuring the total time, you can get the fall time for one drop accurately.
c. The best simple method of measuring g is to use a pendulum, which combines both principles of effectively reducing g and integrating the time. Measure T = pÖl/g, and discuss air friction error and the small amplitude assumption.
4. The falling board. A board is hinged at one end, and weighted at the center, so the center-of-mass is clearly at the center. Thus, the free end will have to fall faster than the free-fall rate. To make the demonstration obvious and dramatic, a cup is screwed to the free end of the board, and an egg is placed further out, on a metal platform. When the support stick is yanked from under the free end of the board, the egg falls faster, and gets the cup to the bottom in time for the egg to fall into it. There is an interesting illusion for the audience: since the eye tends to focus on the fee end of the board, it appears to the observer that the egg jumped backwards into the cup, rather than falling straight down. (This is not so effective for the operator, who is standing too close.) We recommend rehearsing with something other than an egg, because the base board may not be level. An optional part of this demonstration is to move the weight out to the free end of the board and show that an object replacing the egg will not fall into the cup since the free end of the board now falls with about the same rate as the object.

E. Linear Momentum
1. Air track. Some visually beautiful demonstrations can be performed using the long air track. Carts of the same mass can be used to demonstrate the simplest momentum laws (one at rest initially or both moving). In the case of having one at rest initially, it is clear to the most primitive student that momentum is passing through the collision! With unequal mass carts, do the simplest case first: let the large cart hit the small cart. Both will move off in the same direction which won't surprise anyone. Then ask the audience what they think will happen if you let the small cart hit the big one. (Caution: to avoid spoiling the surprise, don't let the carts bounce off the end of the air track and come back at each other when doing the first part of the unequal-mass demonstration.)
2. Firecracker cannon. A firecracker cannon is mounted on a cart, and the velocity of a bullet can be inferred from measuring the recoil velocity of the cannon. Put a cardboard or ceiling-tile target against the wall. Fire a metal bullet first, time the recoiling gun over 1 m distance, and calculate the recoil speed, and bullet speed from conservation of momentum. Repeat with a wooden bullet. Then ask the audience what they think the recoil would be like with no bullet loaded. Measure it. One feature of this demonstration is that it is possible to point out the difference between momentum and kinetic energy. Calculate the kinetic energies of the two bullets, and you will see that the one with the greater KE buried itself deeper in the ceiling-tile target. On the other hand, if you have a free-standing target, the bullet with the greatest momentum will knock the target backward more. So, for doing damage to the target, KE is important, and for knocking the target down, momentum is important. The second part of this demonstration involves putting a second cart on the air track with an open coke can taped to it, to catch the bullet. If all goes well, the audience see the gun recoiling with the same velocity as the coke can, since the two carts are the same total mass. Sometimes the bullet hits the coke can so hard that it tilts the cart enough to make it hit the surface of the air track, and it loses all its momentum. Greater air flow may help, and rehearsal is advised.
3. Skateboard cart. A fire extinguisher is used to propel the instructor on skateboards. Note that the instructor continues to move even when the fire extinguisher is turned off. If you have enough space, you can stop yourself by pointing the fire extinguisher in the opposite direction. The materials for this demonstration are all borrowed when needed, with some effort, but we hope to have our own setup by the end of the year.
4. Ballistic pendulum. The Cenco ballistic pendulum uses a metal ball fired by a spring-loaded gun, and words well if you can get it adjusted properly so that the ball will stick into the pendulum without bouncing out. It is good to precede the pendulum part of the demonstration with two cruder methods of determining the speed of the ball. a. Pull the pendulum out of the way and fire the ball across the room and estimate the time and distance visually, and calculate the speed. (One second and four meters is typical.) The gun has to be oriented so that the ball does not hit the lecture table surface as it is moving forward. b. Repeat as above, but this time calculate the time by measuring the distance from the gun to the floor (vertically) and use t2=2d/g. Measure the horizontal distance and calculate v=D/t.
5. We have a bow-and-arrow ballistic pendulum. With the bow-and-arrow setup, it is also possible to measure the force-versus-distance characteristic of the bow and to calculate the work done on the arrow, approximately. 6. Newton's balls, This is the common apparatus with five balls suspended on strings. If one is pulled back and released, one ball from the other end flies out from the collision. And so forth...

F. Angular Momentum
1. Stand on the rotating stool with weights in both hands, and give yourself a start. By pulling in the weights, or pushing them outward, you speed up or slow down, in accordance with conservation of angular momentum.
2. Stand on the rotating stool with a spinning bicycle wheel in your hands. When you rotate the bicycle wheel, the stool will rotate. You can start this demonstration either with the bicycle when axis horizontal (zero angular momentum about the only free axis of the stool), or with the bicycle wheel axis vertical (maximum angular momentum about the only free axis of the stool).
3. The spinning bicycle wheel can be held aloft on the palm of your hand while you talk. It can also be mounted on a counter-balanced stand. The most effective demonstration is to hang a rope from the ceiling, and put the tip of the axle of the bicycle when in a loop at the free end of the rope. The audience is amazed to see the axle remain horizontal, without falling. The wheel presses around the rope. There are some practical applications worth mentioning: why large aircraft do not start their wheels spinning before touching down on a runway; why a two-engine aircraft might have counter-rotating propellers; and why helicopters are hard to control until you get used to the peculiar reactions.
4. Aircraft gyroscope. We have an old aircraft gyroscope in which the motor is the gyroscope, and there are scales for indicating changes in direction of the case. We have operated it on 15 V so far, but it would probably do better on a higher voltage yet to be determined.
5. Suitcase. We have a flywheel in a suitcase that is fun, if you can get a student to pull it off the lecture table and walk around with it. It is run up to speed with a separate motor and V-belt. At this writing the bearings are shot; it runs down in about 30 seconds. But we hope to have a better one eventually.
6. Loop-the-loop. A ball rolls down a V-shaped track, traverses a vertical circle, and rises on the opposite side of the track. A visually pleasing demonstration of the trade-off between kinetic and potential energy, but quantitatively it's not great because of friction. If you calculate the initial height needed to enable the ball to stay on the track upside down at the top of the loop, you will find that the ball needs greater height in practice (even if rotational KE were accounted for). The students like it.

II. Sound

A. Waves. We have several different kinds of springs, ropes, and rubber hoses to demonstrate waves. Tie one end of a spring to a fixed point and start by sending a single pulse down the spring by jerking your hand or by plucking the spring. The pulse will travel down the spring, reflect, and return. The idea of a standing wave can be lead into by sending a second pulse down the spring about the time that the first pulse hits the end. The class will be able to see the two pulses pass back and forth through each other. Then, with rhythmic pulsing, a standing wave can be produced. With a Slinky, good compressional waves can be demonstrated. We also have a motorized rope shaker which is good for demonstrations of standing waves of various wavelengths.
B. Tuning forks. Can be used with resonance boxes. There are also some flat bars available on resonance boxes.
C. Oscilloscope. Useful in connection with all sound demonstrations so that the waveform can be seen. We have a high-impedance microphone for use with the oscilloscope. Audio oscillators and speakers are available, and are particularly useful in demonstrating the range of audible frequencies. The wave is clearly visible on the oscilloscope even when beyond the range of hearing.
D. Synthesis. We have a Pasco synthesizer with a 440 Hz fundamental. You can vary the phases of the fundamental and the many harmonics as well as their amplitudes. It can be used with a scope to illustrate Fourier synthesis, or with the scope and speaker simply to demonstrate the importance of harmonics in tone quality.
E. Instruments. We have a tape recording of many different musical instruments, and the comparisons of their waveforms on a scope is interesting.
F. Wooden xylophone. Hand-held and simple, and interesting.
G. Organ pipes. Wooden organ pipes are available which can be attached to the air lines in the lecture halls. Both pipes are adjustable in length of the cavity, and the notes are labeled. Too much air pressure will force the resonance into the second harmonic. This effect is interesting to watch on the oscilloscope (using a microphone). Apparently this is a problem for flute players.
H. Bell in a vacuum. We have a bell hung in a bell jar to show that sound cannot travel through a vacuum. The only problem with this demonstration is that the vacuum pump makes more noise that the bell, so the system has to be absolutely leak tight, allowing you to pump out the bell jar, valve it off, and turn off the vacuum pump.
I. Donald Duck. Breathe helium and speak to the class. The higher speed of sound in helium (approximately 3x) resonates higher frequencies in your vocal cavities. For best results, exhale completely, take a deep breath of helium, exhale that, and inhale deeply again with helium, quickly. This way, it'll last quite a long time.
J. Interference and beats. Set up two audio oscillators with two speakers, with similar frequencies. Show on the oscilloscope either using a microphone of by feeding the audio oscillator signals directly into the oscilloscope.

III. Fluids and Pressure

A. Pressure
1. Crushing can. Attach a vacuum pump to a 5-gallon steel can. The can will collapse dramatically. Pass the collapsed can around the class so they can feel it. The steel used in the 5-gallon cans is impressively strong.
2. Bed of nails. This is the best-liked demonstration of all. Arrange with Stu Ryan to lie on the bed of nails, and break a concrete block on his chest, while wearing a black hood. Stu can quote figures regarding his weight, number of nails, pressure, etc. He also has a corollary demonstration showing that it is hard to break a balloon on the bed of nails.
3. Magdeburg hemispheres. Pump out the air between the hemispheres and let students try to pull them apart. The main problem with the hemispheres is that the flanges get messed up when someone drops them on the floor, and then they won't hold vacuum. Please be careful!
4. Water level. The apparatus has several glass tubes of different shape with colored liquid in them, and is supposed to show that the liquid level is independent of the shape of the container. Part two: Tilt the apparatus, put a cork in the end of the tube of one of the containers; when you straighten the apparatus out the water level in the corked container will be higher than in the others. Ask the class why.
5. Manometer. A mercury or oil manometer can usually be found somewhere around the building, and is useful since all discussions of atmospheric pressure involve the U-tube manometer at some point.
6. Coke can. A cute variation on the crushing can demonstration. Put about 1/4 inch of water in an aluminum soda can and heat over a Bunsen burner until boiling furiously, holding the can with tongs at the top of the can. Then invert the can, letting any remaining water run out, and tough the top of the can (the end with the opening) to the surface of a pan or beaker of water. The can will collapse instantly, usually with a popping sound. Failure of the demonstration can be caused by either not waiting until the water is boiling completely, or by not holding the can exactly vertically into the cold water. (If not vertical, it's possible that the can won't collapse but instead will suck water up into the can.)
7. Kinetic model. We have a motor-driven apparatus with plastic balls in it to demonstrate the pressure increase (on a piston) as the simulated gas is heated. Similarly, you can push down on the piston with your hand and the kinetic energy of the balls will be seen to increase. The only problems with this demonstration are (a) the plastic tube housing the balls is getting badly scratched up, and (b) pieces of broken balls sometimes get wedged between the plastic tube and the rotating bottom, which freezes up the motor. The solution to (b) is to loosen the screws holding the plastic housing and rotate the base until the wedged piece is freed; a more ambitious chore of removing all the balls and separating the good ones from the broken ones is required every few years.

B. Fluids
1. Silly putty (silicone rubber). We have a big piece of silicone rubber which is used to demonstrate that the definition of a fluid involves the size of the container and the time scale of the experiment. A ball of silicone rubber bounces, and seems like a solid at times: pulled quickly, it will snap; pulled slowly, it will simply stretch. Recommended: Use the silicone rubber at the beginning of the class to talk about the definition of fluids, and then leave it on the edge of the lecture table, with perhaps 1/3 of its mass sticking out over the edge of the table. During the 30-45 minutes remaining in the class, the silicone rubber will drip over the side of the table. In a longer class, almost all of the silicone rubber will end up on the floor.
2. Buoyancy. Attach a graphite block to a newton scale and weigh it in air. The lower it into a beaker of water and weigh it while submerged, and determine the buoyant force. Ask the class if the buoyant force
of the air, neglected in the initial weighing, is ever important. 3. Old Faceful. An artificial geyser can be set up, heated by Bunsen burners, and will shoot a jet of water and steam up to the ceiling about every 5 minutes, depending on the intensity of the heat. The apparatus takes about 20 minutes to heat up initially.
4. Boiling water. Put water in a flask and put a cork with a tube through it in the end of the flask. Attach a vacuum pump to the tube, pump out the air, and the water will boil. If pumped on long enough the water will noticeably cool. We hope to have a more elaborate apparatus someday with a valve and a vacuum gauge attached so that you can determine the vapor pressure of the water at room temperature.
5. A plastic bag filled with hot water will float in an aquarium. A plastic bag filled with cold water will sink in an aquarium.

C. Fluid Dynamics
1. Flow tube. A glass tube with different diameters incoming and outgoing has a U-shaped manometer attached between the two tube sizes, and colored water is in the manometer. When air flows through the tube, the water levels in the manometer shows that the pressure is less in the small tube than in the large tube. Caution: Too much air flow eject the water.
2. Lifting disk. Air is sent through a tube to the surface of a flat disk and flows out along the top surface of the disk. The resulting reduced pressure allows the disk to be lifted.
3. Floating ball. An air jet is used to suspend a ball in midair. Air flowing around the ball causes reduced pressure which tends to restore the ball to the center of the stream of air if it wanders. Moving or tilting the air jet enables you to move the ball as well. The air jet may be tilted to nearly horizontal at times. Some balls work better than others. A ping-pong ball is too light. A tennis ball is too big. A 1- 1/4 inch wooden ball is good, and a golf ball is good (though slightly heavy). A lot of air pressure is required for good results (90 psi).
4. Beach ball. A wind tunnel blower is used to support a beach ball. This demonstration is particularly effective when the blower is tilted (at about 45 degrees); the beach ball can then be sent out across the room (even into the hallway) by increasing the air flow, and brought back. The new low ceilings limit you. Can be opperated with or without the restrictor to show a difference in effect.

IV. Thermal Physics

A. Heat
1. Linear expansion. An aluminum rod is heated with a torch, usually using the oxygen-natural gas torch. As it expands, it raises a wooded rod, and a scale at the end of the rod indicates the temperature of the rod. Ice cubes can be used to cool the rod quickly.
2. Ball and ring. A torch is used to heat up a metal ring so that a metal ball can easily pass through it. The clearance is negative at room temperature.
3. Radiation. Pass a current through tungsten wire, or use a resistance heater, to illustrate the radiation from a hot body. Make the point that the spectrum is independent of the material. A second version of this demonstration is to use a torch to heat up a piece of metal and a fire brick, so that they both glow red. All of this is best done with the lights out.
4. Convection. A glass tube is formed into a rectangular path, with an opening at the top, and is filled with water. A thick dye is added at the opening, and heat is applied to one bottom corner of the rectangle. Convection causes the dye to circulate.

B. Liquid Nitrogen Tricks
1. Boiling. To prove that LN2 is boiling at room temperature, pour some into a whistling tea kettle, and sit it on the lecture bench. If possible, place the kettle on a block of ice or even dry ice.
2. Boiling. Pour LN2 on your hand and explain why it doesn't hurt. Pass a dewar of LN2 around the class.
3. Cannon. A pipe is capped at one end. Slide a test tube filled with LN2 down the open end and quickly cork the open end - the more tightly the better. Let the LN2 run out into the pipe and the pressure will blow the cork out. 4. Spray. Stick one end of a latex hose down into a dewar of LN2 and the boiling action will blow LN2 and vapor out the other end. Spray the class.
5. Snake. Stretch a latex tube over the end of a meter stick and insert the tube and meter stick into an LN2 dewar and hold them there until the latex tube is completely frozen and the LN2 stops boiling. Remove the latex from the LN2 and place it on the lecture bench. As the latex warms up, it will move around on the lecture bench.

C. Change of State
1. Deflating balloon. Blow up a balloon, put the end over a test tube, put the end of the test tube in a dewar of LN2, and the air in the balloon will condense into liquid. The class can see the liquid air when you remove the test tube from the LN2, but only for a short time, as the test tube frosts up, and the balloon re-inflates.
2. Inflating balloon. Pour LN2 into a test tube and quickly slip a balloon over the open end of the test tube, and rest it in a beaker. The balloon will inflate, and possibly fly off the end or break.
3. Nitrogen trioxide. A flask filled with N203 (and sealed) is available. When the end is inserted into an LN2 dewar, the gas slowly condenses. The only reason for doing this is that the gas is a pretty orange color, and the liquid is a bright blue color, unlike the colorless substances normally dealt with.
4. Banana hammer. If a banana is frozen slowly in an LN2 dewar, it gets hard enough to use to hammer nails into a 2x4. Often the banana cracks and falls apart, but the class likes it anyway. Maybe there's a better vegetable that won't crack so easily during freezing. It takes more effort, but a mercury hammer can be made popsicle style, and it lasts a long time.

V. Electricity and Magnetism

A. Electrostatics
1. Charges. Use the blue rotating stand to hold glass or rubber rods, charged by rubbing with wool, and show repulsion or attraction by bringing other charged objects nearby. Positive is defined as glass rubbed with silk. Negative is defined as rubber rubbed with fur. Anything else can be determined by comparison. Try leather, wood, and your finger, rubbed with cloth or fur.
2. Van de Graaff. Several demonstrations with a Van de Graaff generator:
a. Use a grounded sphere nearby to determine the longest spark possible. Breakdown in air occurs at 30,000 V/cm in dry air, and less in damp air, so you can determine an upper limit to the voltage generated by measuring the spark length.
b. Tape string or hair to the Van de Graaff sphere, and the strands will separate when charged. Bring a grounded rod near the sphere, and the strands will move around as the charge distribution is altered.
c. When a rotator shaped like a lawn sprinkler is put on top of the Van de Graaff sphere, it will rotate as charges are repelled off the tips of the rotator.
d. Sprinkle paper bits on the Van de Graaff sphere. When the sphere is charged, the bits of paper will fly off. For the best snow-like result, hold a grounded rod on the sphere until the Van de Graaff motor has gotten up to full speed, then pull the grounded rod away rapidly.

B. Electricity
1. Electric field. A candle is mounted between two metal plates, separated by 3 or 4 cm. When a voltage is applied between the two plates, the candle flame bends toward the negative plate, since the positive ions are heavy and form the visible part of the flame. Electrons travel to the positive plate. It takes roughly 1000 V to bend the flame completely into the negative plate.
2. Tesla coil. High frequency electric effects can be shown with either the large Tesla coil or a hand-held one. Draw sparks to a metal object in your hand. Hold a fluorescent bulb in your hand and touch one end to the Tesla coil. Use the Darth Vader wand (a fluorescent bulb that fits into the hand-held Tesla coil). Use the "neon wand" lit in a similar manner as the fluorescent bulb. We have an attachment for the large Tesla coil that holds an incandescent bulb, and if you run your finger over the surface of the bulb, students can see a spark inside the bulb from the filament to your finger.
3. Jacob's ladder. Use large neon sign transformer with vertical diverging wires attached to create a spark that climbs upward. Run a piece of paper through the spark and pass the paper around to the class. The paper will have a line of holes burned in it, showing that the spark is not continuous, but turns on and off 120 times per second.
4. Currents. Use a big dc power supply to pass 15 A of current through an aluminum rod, and hold the rod in your hand to show that the current doesn't affect you (voltage around 0.2V). Determine resistance. Repeat with some carbon resistors, of different wattages, to help explain the problem of burning out resistors.
5. Resistance. Use a resistance meter to measure the resistance of various items - carbon resistors, light bulbs, human body.
6. Tungsten wire. Use a variac to pass a current through a piece of tungsten wire, simulating a light bulb. As the current is slowly increased, the wire glows brighter until one part glows white hot and burns out. The demonstration suggests:
a. the light bulb works best with a vacuum around the filament, and
b. it's a good way to make a fuse.
7. Light bulb circuits. Use a variac with lamp sockets for three demonstrations:
a. With one socket containing a fuse, put a clear-filament light bulb in the other socket and determining
V, I, R, and P. A current measurement is required, using a clamp-on device, for example. Repeat for 40, 60 and 200 W bulbs. Which has the smallest R? Use a small fuse (e.g., 0.5A) with the 200 W bulb to demonstrate a fuse.
b. Put two bulbs in the series circuit and explain the effects observed. Measure and calculate Reff.
c. Rewire the sockets for parallel operation and repeat (b).
8. Power meter. Operate the light bulb demonstration with the standard line power meter in the circuit, and explain how the eddy current motor words. Explain kilowatt-hours, etc.

C. Magnetism
1. Poles. Use the blue rotating stand with bar magnets to show repulsion and attraction. The basic idea for a motor can be demonstrated at this point, by moving one magnet around in a circle with your hand, and letting the other one follow. Ask the class where the energy is coming from. Magnetic?
2. Electromagnetism. Use the big dc power supply to put 15 A through an aluminum rod. Hold the rod over a bar magnet mounted on the rotating stand. The magnet will line up perpendicular to the rod. Reversing the current will reverse the magnet direction. Use a loop of wire containing at least 10 turns in a similar manner to show how the current can effectively be amplified by using many turns.
3. Parallel wires. Use the blue apparatus containing two parallel wires with a reversing switch, along with the big dc power supply, to show the magnetic interaction between current-carrying wires.
4. F=BIL. There is a small apparatus in which a rod can roll along two metal rails between the poles of a horseshoe magnet. The big dc power supply is used to pass a current along the rails and through the rod. Reversing the current causes the rod to roll the opposite direction. The only problem with this demonstration is that the magnetic field is weak and it takes as much as 10 A to get the rod rolling, and if the contact is not good, sparks weld the rod to the rails. We will probably make a larger version of this apparatus someday.
5. Jumping coil. Use one of the very strong magnets to make a loop of wire jump out of the field when a current is passed through the loop. The loop should be lightweight and consist of at least 10 turns. Put a big wad of paper under the gap of the permanent magnet to let the loop rest in the center of the gap. Turn the current on quickly. (Using our present dc supply, you do this by setting the variac at its maximum and "switch" the unit on by plugging it into an outlet when you want the coil to jump up.) Obviously, you have to test the setup first to make sure the current is passing in the correct direction.
6. Lorentz force. Use the discharge tube that has a fluorescent strip in it so that you can see the electron beam. Use a horseshoe magnet to bend the beam up or down. 7. Induced current. Attach a loop of wire to an electrometer and wave it in a magnetic field to generate a current. This demonstration works best if the electrometer has a center zero, so the class can see that the current passes one way and then the other, as you move the coil back and forth in the magnetic field. If the electrometer is sensitive enough, this demonstration will work even with the earth's magnetic field.

VI. Electromagnetic Waves

A. Electromagnetic Spectrum
1. This is a very long demonstration that can take two class periods, and is actually many small demonstrations. It is designed to show why we break the electromagnetic spectrum into many parts, according to how the waves are generated and detected. The demonstration strives to give an example of each part of the spectrum.
a. Extra Low Frequency. Mechanical generator. Attach a wire to an oscilloscope to show the 60 Hz waves that are passing through the lecture hall due to the power lines, and that energy is indeed being transported. Note that the wavelength is half the distance from the earth's equator to the pole.
b. Audio Frequency. LC circuits. Use an audio oscillator with a wire attached as an antenna to transmit an electromagnetic wave to an oscilloscope (which also has an antenna attached). Note that the signal is stronger if the antennas are closer. At the higher end of the audio oscillator frequency range you can pick up the tones on an ordinary am radio. Calculate wavelengths.
c. Radio Frequency. LC circuits. Show the antenna coil and tuning capacitor in a receiver. Also show how radio-frequency noise can be picked up on a oscilloscope antenna when a discharge occurs (using a tesla coil, for example), and explain how these electromagnetic waves are produced.
d. Microwave Frequency. Too fast for LC circuits; need free electron motion. Show a magnetron tube and explain. Use the microwave apparatus from the junior-senior lab to demonstrate microwave transmission. Note that the receiver has no power source; movement of the meter needle is proof that energy is being transmitted across the space separating the transmitter and receiver. Note that the much greater frequency of microwave (and visible) radiation allows more information to be transmitted (number of pulses per second) than by audio or radio frequencies, if you can handle the modulation. Molecular rotation frequency.
e. Infrared Frequency. Molecular vibrations. Show a red-hot resistance heater. Discuss the ir radiation given off and absorbed even by room temperature objects. CO2 laser lines.
f. Visible Frequency. Outer electrons in atoms making transitions. The laser is a good example for a demonstration, or a discharge tube.
g. Ultraviolet Frequency. Outer and inner electrons in atoms making transitions. Use a black light, and explain fluorescence. Show fluorescent chalk. Shine the black light on a beaker of antifreeze and explain how it helps looking for radiator leaks in a car. We have a demonstration fluorescent lamp in which one side is uncoated so that you can see the pure mercury spectrum, and the other side is coated with the usual fluorescent material so that most of the ultraviolet light is absorbed and the energy is re-emitted as visible light.
h. X-ray Frequency. Deceleration of high energy electrons, and inner-shell transitions of electrons in atoms. We have an old X-ray tube which no longer works, but is interesting to see, and it is exactly the kind that used to be used in dentists' offices, etc. The walls of the tube are discolored due to sputtering of the anode material.
i. Gamma-ray Frequency. Nuclear transitions. We have some radioactive salts, and a gamma-ray source that can be used with a Geiger counter. In all of these cases, discuss the fact that the stronger the force involved, the more energetic the photon.

B. Light
1. Laser light show. We hope to develop over the years a laser light show. At this writing all we have is a set of mirrors on speaker cones driven by audio oscillators so that you can show Lissajou figures on the wall.
2. Multimode interference. Use a lens of any kind to broaden a laser beam spot on a wall. The speckle pattern is due to interference. If you move the lens around, you can locate dust or imperfections in the lens which will cause ring interference patterns to appear on the wall.
3. Young's double slit experiment. Use the Pasco setup from the 1300 lab, with laser and photoetched slits, to show the interference pattern on the wall.
4. Polarization. Use the Pasco setup from the 1300 lab. We also have polarizers mounted on cardboard (with diffraction gratings also) that you can hand out to the class, if the class is of reasonably small size.

C. Optics
1. Blackboard optics. We have the blackboard optics kit and accessory kit.

VII. Atomic and Nuclear Physics

A. Atomic
1. Atomic spectra. Pass out cardboard spectroscopes to view:
a. sunlight;
b. fluorescent lights;
c. demonstration fluorescent lamp (half is uncoated, giving pure mercury spectrum, and half is coated, whence one sees the mercury spectrum on a continuous background);
d. spectrum tubes, of which we have about a dozen with different gases, and hope to have these mounted on a board soon. They can be excited with a Tesla coil.
2. Gas discharge excitation. We have a gas discharge tube which may be attached to a vacuum pump. As the air is evacuated the discharge approaches a glow discharge (which will get weak if the pump is good enough). Excite with a Tesla coil. Put in a couple of drops of solvent (acetone, etc.) and repeat; the color will be different.
3. Geissler tubes. A Geissler tube set will be mounted on a board soon, and can be excited with a Tesla coil. They show that the discharge can go around corners. Mainly, they are pretty.
4. Discharge tube set. These are the various tubes in a green wooden rack. Most show that the current- carrying particles are negative.
5. Laser. For discussions of the operation of lasers, we have an old defunct one dismantled so the students can see the laser tube and the power supply. If you touch a Tesla coil to the laser tube it glows, but doesn't lase (in most cases gas has leaked in or out).
6. Gas balloons. Fill two balloons with H2 and two with He, and tie them above the lecture table. Touch a match to them sequentially and see if the students can guess which were H2 and which were He. This demonstration is mainly for fun, but can be tied into a discussion of chemical reactions, activation energy, etc.
7. Sodium. Drop a small piece of sodium in a flask of water. If large enough it will catch fire, and may pop if enough H2 builds up. A suitable piece is maybe 4 mm on a side. Larger may be dangerous.
8. Photoelectric effect. The Braun electroscope can be used in a good demonstration of the photoelectric effect. Charge up the electroscope negatively, and shine a uv light on it. It will slowly discharge. A good mercury lamp may be obtained from the junior lab. The experiment works best is if an aluminum disk is attached to the top of the electroscope. If the desk is oxidized (or is some other metal) I can't guarantee anything. Sandpaper the disk. If the electroscope is charged positively, the uv lamp has no effect.

B. Nuclear
1. Radioactivity. Use the scaler and Geiger counter to observe radiation from the sample supplied with the scaler set, and to observe radiation from the six salt samples we have available (three are non- radioactive).
2. Absorption. Same as in (1), but put cardboard, aluminum, and lead sheets between the source and detector. The students also like to see you put your hand in there.