This demo consists of a small ball bouncing off a larger ball when both balls are dropped together.
A demonstration of the formation of the solar system or the collapse of a star to a neutron star may be done by using the turntable with weight. A spinning student with weights in her outstretched arms stands on a turntable and brings her arms in. Make sure the student starts off spinning slowly since angular momentum conservation causes the student to spin faster as her arms are brought in.
A gravity well is attached to a rotating platform and spun to simulate binary star systems.
There are two celestial spheres available.
There are various desktop planetarium programs available that can be used with a video projector. These programs can demonstrate the night sky, an orrery of planet motion, retrograde motion, eclipses, etc.
An Earth globe, Moon ball and light bulb for the Sun can be used to demonstrate Moon phases, eclipses, umbra and penumbra.
Two magnetic foci and several different loops are available for drawing ellipses on the blackboard.
- A lead ball at the center deforms an elastic membrane which changes the orbit of a plastic ball. It can be used as a demonstraction of Einstein's general relativity.
- A model of the way gravity distorts space around a heavy object.
The partial pie plate [2]is a good example of what would happen to a satellite if suddenly its host which provides the gravitational force is removed.
Students can see the spectral lines of hydrogen by looking at a arc tube on the lecture table through replica gratings. Several students can come down at once and look. You can also project the spectrum of mercury on a screen for the whole class to see: Projected Mercury and Continuous Spectra [3].
The Frank-Hertz experiment [4] above shows atomic energy levels, but it is a very complicated demonstration.
Finally, a very simple demonstration of energy levels is fluorescent and phosphorescent materials with an ultraviolet light. The energetic UV light kicks the electrons up into high levels, and as they jump part way down immediately (fluorescent) or with some seconds of delay (phosphorescent with partially forbidden transitions), the electrons emit visible light of various colors.
Doppler Shift of sound is dramatically demonstrated by swinging a ringing tuning fork around your head.
The whistle ball is another good way to demonstrate doppler shift. A sponge ball has been stuffed with a battery operated whistle in its core. As the ball is thrown around the lecture hall, the students hear a shift in the ball's frequency.
The action of a diffraction grating itself can be demonstrated by passing a laser beam through the grating and showing the spread out spots on the wall. You can lead into the phenomenon by showing the effect of Single, Double, and Multiple Slits [5] with the Cornell plate. Interesting effects result from crossing two gratings in the laser beam, or by arranging many at all different angles.
A hydrogen arc tube can be viewed with a large holographic grating. Also available is an incandescent light which can be used to look at a continuous spectrum.
Another option is that students can use individual gratings to see the spectral lines of hydrogen.
A hollow prism filled with carbon disulphide will disperse white light into its component colors. Other glass and lucite prisms are available, but their dispersion is not as great as CS2.
A sodium lamp is arranged to shine on a rear projection screen. An ordinary flame, say of a match or Bunsen burner introduced between the lamp and the screen will not cast a shadow, but if a wire or stick dipped in salt solution is placed in the flame, a dark shadow of the flame appears.
Arc tubes of hydrogen, helium, argon, mercury, and a few others can be viewed three-at-a-time with a large holographic grating. Also available is an incandescent light which can be used to look at a continuous spectrum.
Another option is that students can use individual gratings to see spectral lines of these tubes.
A light bulb with a long filament is powered through a variac on the overhead projector. When the filament is turned down, it looks black against the bright light of the overhead. Then the overhead is turned off and it is shown that the filament is actually glowing and emitting light.
Below are links to suggested demonstrations for Newton's First Law.
A good way to demonstrate Newton's second law is with the Pasco dynamics track [12].
The following demos are recommended to demonstrate the consequences of Newton's Third Law: for every action there is an equal and opposite reaction.
A continuous cloud chamber shows tracks of charged particles. Advance notice is needed to obtain the dry ice necessary to operate the chamber. Thoron gas (thorium emination, Rn 220, half-life = 1 min.) can be blown into the chamber to produce alpha particle tracks. Since the daughter nucleus Po 216 with a half-life of 0.15 sec. is also an alpha-emitter, two pronged tracks will be seen in the chamber. A needle with Pb 210 also produces a-tracks. Two to five students look at this demonstration at once so it is best to arrange a little time at the beginning or end of class for them to come down and look.
Cloud Chamber
Methanol evaporates from the trough, and the vapor falls toward the cold dry ice (-100 F = -73 C). In the process the vapor is super cooled; that is, cooled below its normal condensation point. When a high speed charged particle from a radioactive source or from a cosmic ray passes through the super cooled vapor, it ionizes the air and methanol atoms along the way; i.e., it strips electrons from these atoms. These ions and electrons serve as condensation centers for the methanol vapor, which condenses out in tiny droplets along the track of the charged particle outlining its path.
The charged particles from the radioactive source are typically helium nuclei (alpha particles). This source is "license free", meaning it is too weak to be considered dangerous by governmental regulatory agencies. Charged particles from cosmic rays are typically protons and muons.
Small "license free" sources of activity < 0.1 microcurie can be taken into the class to activate a small hand held counter. Cloud chamber alpha sources of lead 210, beta souse of strontium 90, and an old Coleman gas mantle which contains thorium 232 are available.
A Gieger-Mueller tube simultaneously connected to a counter, an analog meter, and an amplifier and speaker will show the activity of the sources in three different ways.
Experiments 8 and 9 in the 8E lab are concerned with absorption of radiation, half-lives, etc.
Heavy water, D2O, molecular weight 20, is about 10% heavier than ordinary water, H2O, molecular weight 18. Identically filled bottles of heavy water and tap water can be compared by hand or on a double pan balance. Of course, deuterium and heavy water are not radioactive.
The kit has been improved with magnetic clamping to the blackboard and a multiple ray projector. Most of the principles of geometrical optics can be nicely demonstrated with this kit
We have a light which magnetically clamps to the blackboard and projects five parallel rays. This dramatically shows convergence and divergence of rays in lenses and mirrors.
The Lenses and Mirrors applet below can be used as an online demonstration.
Physlet by Wolfgang Christian webPhysics, Davidson College [16]
Instructions on how to use the animation:
A small inverting astronomical telescope can be shown to students individually.
A large parabolic mirror is available to show image formation and to demonstrate how telescopes are used for gathering images.
This demo shows the shifting colors as a function of filament temperature. Also, this demo shows prism dispersion, radiation intensity as a function of wavelength, and infrared radiation. The black body radiation curve can be demonstrated by using a radiation sensor hooked to a digital millivoltmeter. The carbon disulfide prism (see Dispersion [17]) is used to spread out the light of a slide projector lamp onto a screen . As you scan across the spectrum with the radiation sensor, the millivoltmeter shows the peak of the 3000 K tungsten filament in the infrared with the tails of the curve in the visible spectrum and further infrared.
The same demonstration can be done more qualitatively. Turn down the room lights and show the spectrum of "white" light on the wall. As you reduce the voltage to the lamp with the variac, the blue color dies away, and then the green, leaving only dull red of low intensity. (Of course, the 3000 K tungsten filament already peaks in the infrared so the initial "white" light is already quite red. Infrared itself can be demonstrated; see Infrared, Radiometer, and Maxwell's Spectrum [18])
The applet below shows the blackbody curve and colors corresponding to the given temperature. |
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A laser beam is arranged to pass through the slits and be reflected onto the overhead screen. Standard demonstrations are single slit diffraction, double slit interference, and diffraction from a circular opening. Two lasers are arranged so that single and multiple slits can be shown simultaneously, one pattern above the other.
We have precision slits etched in metal foil. The slit widths and spacings are marked. The most useful single and double slits have a width of .04 mm. The double slit spacings are .125, .250, and .5 mm. There is also 3, 4, and 5 slits with the same width (0.04 mm) and spacings of .125 mm.
Hair, CD's and DVD's can be used as diffraction gratings. Simple measurements of the first maximum gives the track spacing. Comparing the pattern from CD's and DVD's gives the ratio of the track spacing for the higher density DVD.
The diffration pattern can be observed with both a red and a green laser simultaneously to show the effect of wavelength. The red laser wavelength is 0.6328 micron and the green laser is 0.532 micron
The Cornell plate, diagrammed below can also be used for these demonstrations. It is clipped to a special stand so that successive slits in each column can be brought into the laser beam by adjusting a rack and pinion knob.
Column (a) Successively narrower single slits
Column (e) Successively wider double slits
Column (b) Single slit starts narrow, becomes wider,
becomes double slit, becomes narrower.Column (d) Go from one slit to two slits to three to four to ten to show sharpening
of the fringe maxima.
The Cornell plate was originally designed to be used (and can still be used) with the individual eye to view a straight filament bulb.
A very simple demonstration of the photoelectric effect is performed with a zinc plate as the electrode of an electroscope. An ultraviolet lamp covered with glass is arranged to shine on the plate. The plate is charged negative with an electrophorus, and the electroscope needle diverges indicating the charge. The blue light of the lamp will not knock out electrons from zinc, but if the glass (opaque to UV) is removed from the lamp, the needle quickly falls as electrons are kicked away from the plate. The zinc plate must be cleaned with steel wool within an hour or so of the demonstration to remove the oxide.
A variation of this experiment has a spiral electrode with a positive voltage in front of the zinc plate with a sensitive current meter to measure the small current of the photoelectrons through the air.
The photoelectric effect is also done as experiment 4 in the 8E lab. The stopping voltage is measured as a function of wavelength (color) of the exciting light, and Planck's constant determined from the slope of the line.
Links:
[1] http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html
[2] https://demoweb.physics.ucla.edu/node/79
[3] https://demoweb.physics.ucla.edu/node/84
[4] https://demoweb.physics.ucla.edu/node/86
[5] https://demoweb.physics.ucla.edu/node/90
[6] https://demoweb.physics.ucla.edu/node/150
[7] https://demoweb.physics.ucla.edu/node/100
[8] https://demoweb.physics.ucla.edu/node/151
[9] https://demoweb.physics.ucla.edu/node/102
[10] https://demoweb.physics.ucla.edu/node/101
[11] https://demoweb.physics.ucla.edu/node/99
[12] https://demoweb.physics.ucla.edu/node/104
[13] https://demoweb.physics.ucla.edu/node/146
[14] https://demoweb.physics.ucla.edu/node/148
[15] https://demoweb.physics.ucla.edu/node/149
[16] http://webphysics.davidson.edu/Applets/Applets.html
[17] https://demoweb.physics.ucla.edu/node/293
[18] https://demoweb.physics.ucla.edu/node/207