How to measure Planck’s constant using an LED
- Measure LED threshold voltage using voltmeter and ammeter.
- LED converts electron energy to photons. Energy lost by electron = energy gained by photon = (electron charge) times (voltage).
- So, if threshold voltage is 2.2 volts, energy of emitted photon must be 2.2 eV.
- Use E=hc/lambda, and measure lambda using Red Tide spectrometer with Logger Pro (see below pic), to determine h. Take data using LEDs of 4 different colors and fit data to line with slope h.
- Hand held spectrometer can be used to view LED spectrum.
Use “Fun Fly Stick” to charge up conductive sheet.
Mylar strands align with electric field.
Place support rods together to form cylinder. Electric field of cylinder points outward radially.
- Located in L01, section A-2
Wire balances on top of battery and is free to rotate. Top of wire touches positive terminal; bottom of wire touches magnet connected to negative terminal. Wire completes circuit and current travels through wire. Direction of magnetic field creates a Lorentz force that causes wire to turn.
Historical significance: First electric motor. First successful model devised by Michael Faraday. See: https://en.wikipedia.org/wiki/Homopolar_motor
- Located in L01, section B-4.
Developed by NASA Scientist Steve Papell in the 1960’s, Ferrofluid is a colloidal liquid made of paramagnetic nano particles. When subjected to a magnetic field, the nanoparticles form regular patterns of peaks and valleys.
For an interesting list of modern applications see:https://en.wikipedia.org/wiki/Ferrofluid
- Located in L01, section B-2 (in bin with iron filings)
Attach noise-maker to battery and insert into styrofoam ball (ball has large slit).
Toss ball (play catch with student volunteer) to hear change in pitch.
- Located in L02, section C-2
Beads change color, temporarily, from white to blue, purple, or red when illuminated by UV light. Use with UV flashlight, or direct sunlight.
See physics here: http://www.arborsci.com/uv-beads-package-of-1000
Flashlight emits UV light, of wavelength 385nm. Contains filter to block white light. Use also on minerals, florescent dyes, scorpions, etc.
- Located in L01, section C-1.
Appearance of egg mimics that of the sky.
Glass egg is translucent, milky white, and contains no pigment- only microscopic particles that scatter light. Short wavelengths of light (blue) have a tendency to scatter off the microscopic particles in the glass; while long wavelengths of light (red and yellow) tend to pass through. The egg therefore appears yellowish red when held in front of a light source, and blue when held in your hand.
- Located in L01, section B-6
Charge teflon rod with fake fur (shown in above photo) by rubbing together.
When charged rod is brought into the proximity of water stream, attraction between water and charged rod will cause stream to deflect.
- Rod and fur located in L01, section A-1.
- Bucket with hole, and tub, located in L35, section G-3.
Copper pipes chime when hit (hang by loop and tap with hard object). Pipes are identical in size and composition, and are therefore identical in pitch.
To see how temperature affects pitch, dip one pipe in liquid nitrogen and cool for 1 minute. Tap both pipes to hear differences in pitch. Caution: DO NOT TOUCH COLD PIPE WITH BARE HANDS. USE CRYO GLOVES.
Pipes located in L02, section C-1. Ask for assistance with LN2.
Lid of plastic bottle, shown above, is a pump, and can be used to pump air into container.
Place empty bottle on sensitive digital scale and record scale reading. Then pump additional air into bottle and re-weigh.
- Bottle and pump located in L02, section B-5.
- Scale in L35, section D-2.
Is the mask in the above image concave or convex? Strangely, it appears convex (sticking out towards you) even when viewed from the concave side. Even more strange: the face appears to turn and follow you as you view it from different angles.
Below is a profile view of the mask.
Illusion works best when mask is illuminated from behind.
In a Big Bang universe, the shape of our past light cone is not strictly conical, but tear-drop shaped. The moment of now is located at the pinnacle of the drop, the moment of the Big-Bang is located at the very base.
To understand why our past light cone has this shape, recall that the distance from a light cone’s surface to its time axis is the photon’s emission distance. All of the photons we see today- from the very early universe- were emitted from regions of space that were, at the time, very close to us. (Spatial expansion caused these regions to separate very rapidly.) So, photons emitted very early in the universe’s history, and photons emitted very recently have small emission distances.
The slope of the light cone represents the recessional velocity of light with respect to our region of space. The fattest part of the light cone corresponds to the moment in time when the photons we are currently seeing, from the Big Bang, first began to approach us.
The model shown above is actually the light cone for a linearly expanding universe (expansion at a constant rate- i.e., recessional velocities do not change with time). The most accurate model for spatial expansion- lambda cdm- is actually very close to this in shape.
When droplet of olive oil (oleic acid) is placed on water, oil spreads out until oil layer is 1 molecule high.
If the oil “spill” radius and the size of the original droplet can be measured, one can estimate the length of the oil molecule.
Volume of original droplet = volume of oil spill pancake.
Use wire loop (diameter~1mm), to estimate volume of droplet (assume droplet is wafer, not sphere). Use calipers to measure.
Dip loop in olive oil.
Remove excess oil using paper towel.
Dust surface of water with lycopodium powder. This allows you to see clearly the final diameter of the spill. The larger the container the better.
Dip tip of wire loop into water. Oil immediately spreads out to form circle (very cool to watch!).
Measure diameter with ruler.
Should get order-of-magnitude accuracy.
- Lycopodium powder and oil located in L35, corrosive materials cabinet (powder is safe to handle).
- Tub located in L35.
- Calipers located in L35, section D-2.
- Tape measure in L35, section A-1.
Heat of friction causes ink in “Frixion” erasable pens to disappear.
Ink reappears when exposed to cold temperatures.
Use lighter for high temp. (Be careful not to burn paper. Just wave flame in front of paper until ink disappears)
Use liquid from compressed air to achieve cold temperatures. (Invert can and spray. Be careful not to get liquid on skin. Extremely cold.)
Heat aluminum blocks to 350 degrees C using adjustable hot plate shown in photo.
Use water dropper (with demo) to place droplets of water onto surface of hot aluminum blocks. Leydenfrost effect causes droplets to hover, and prevents them from evaporating immediately.
Droplets on the ridged block are propelled along the surface- from right to left in above photo.
Raise one edge of the hot plate slightly, so that droplets on smooth surface slide down while droplets on the ridged surface climb up.
See more about this here: http://www.wimp.com/when-water-flows-uphill-the-leidenfrost-effect/
Light, of high enough frequency, will cause quinine (found in tonic water) to fluoresce. The emitted light is a brilliant blue color. Also works with a black light.
Location: Tonic water and violet laser pointer in L01, section B4. Black light in section A1 (or A2).
When platform is rotating, cannon misses target. When not rotating, cannon hits target.
Located in L02, section D3
Cannon located in section B3
Located in L35: Below, and to the right, of the sink.
For information about exciting and interesting infrared technologies and applications see: http://coolcosmos.ipac.caltech.edu/infrared_world
Click here to watch the ball-drop race.
- The ping pong ball starts off in the lead but is slowly overtaken by the heavy, steel ball.
Few demos are as simple and surprising as this one.
- Chain appears to levitate as it falls out of cup.
- Elevate cup above floor 5 to 7 feet. Pull end of chain out of cup to begin initial descent. Chain will self-siphon.
- While the chain falls at an accelerating rate, a standing wave develops above the lip of the cup and levitates.
- See a brief youtube video here.
- See a slow-mo video here, with a conceptual explanation.
Located in L02, section B-3.
- When current through a solenoid changes, a magnetic field is induced within the solenoid. If two solenoids are concentric with each other, the induced field in one solenoid produces a changing current in the other.
- Connect a power supply to one solenoid and a galvanometer to the other.
- Unless steel rod is inserted in innermost cylinder (shown above), induced magnetic field is too week to produce a noticeable effect. Steel rod greatly enhances effect.
Solenoids: L01, section
B-2Galvanometer: L35, section F-3
Power supply: L35, section F-1
- Principle: Static electricity is cool.
- Located in L01, section A2
- Van de Graaf accessories are located beneath Van de Graaff
generator in plastic containers.
Some ideas for experiments beyond the typical shock-myself-and-my-students:
- Bend a paper clip into an L shape and tape it to the charged sphere to create
an ion gun; point the paper clip at the palm of your hand to feel the “ion
wind”. Point the paper clip at your shirt to charge your shirt up- after
30 seconds shirt should begin sticking to your chest.
- Place a cup of styrofoam peanuts, or a stack of styro or aluminum plates
on top of the sphere, turn on generator and watch stuff fly.
- Dim the room lights, touch one end of a fluorescent bulb to the charged
sphere and the other end of the bulb to the small discharging sphere. Bulb
- Using a squirt gun shoot a stream of water past the charged sphere; water
should ionize and stream will disperse.
Additional Van de Graaff demo ideas
Located in L35, section H-3.
Very nice (and expensive) demo. Please handle with care.
For detailed operation instructions see Instructions booklets-
one for fuel cell stack, and one for electrolyzer.
- Connect fuel cell stack to electrolyzer as shown in above picture.
- Fill tall cylinder with distilled water up to the 0 cm mark.
- Fill the water reservoir of the electrolyzer with deionized water up to the -A- mark.
- Connect the power supply, or solar cell, to the positive and negative terminals of the electrolyzer. Current causes water to split into oxygen and hydrogen. The oxygen escapes into the atmosphere, and the hydrogen accumulates in the gas storage tank (tall cylinder).
- When hydrogen gas is allowed to flow into the fuel cell stack (see fuel cell operating instructions booklet; pg 9), the voltage difference that develops across the stack can be used to power the fan (see above picture).
- Also, the voltage difference across each individual cell can be measured with a volt meter.
For Demo and Lab ideas see “Fuel Cell Technology for Classroom
Diffusion Cloud Chamber
- Pasco Diffusion Cloud Chamber is very easy to set up and operate. Does not require the use of dry ice or liquid nitrogen.
- Use pump to circulate ice water through base. Peltier device cools chamber base down to -35 C.
- Soak paper liner with isopropyl alcohol (93% or higher), and pour alcohol into bottom of chamber, about 1 mm deep.
- Cloud sets up in 10-15 minutes. Cosmic ray tracks (mostly thin streaks) should readily appear.
- Use radiation sources to see alpha particle tracks (fat streaks).
- Needle source is lead 210; disk source is americium 241 extracted from a smoke detector.
- Footage of this cloud chamber in operation: https://youtu.be/1ss5DBGWMo4
- Located in L01, section C1.
Petri dish cloud chamber
- Soak the black paper with ethanol or highly concentrated isopropyl alcohol (93% or higher).
- Insert the radioactive source (Pb-210) into the hole of the side of the container.
- Place the chamber on a slab of dry ice.
- After 5 or 10 minutes of cooling down, clouds of supersaturated alcohol will form near the bottom of the container. Alpha particles or cosmic rays that streak through the alcohol cloud ionize the alcohol and cause it to condense along the particle’s path. These tracks are visible.
- To illuminate the tracks, and make them more visible, shine a flashlight (or cell phone light) into the side of the container.
- Getting the alcohol cloud to form is a little bit tricky. Before attempting this demo in class, try it out.
Located in L01, section C1.
Demonstrate why the sky is blue and sunsets are red.
- tank, water, artificial creamer, flashlight (pretty simple!)
- Use polarizer to show that scattered beam is polarized.
- Located in L01, section B6.