lecdem.physics.umd.edu

ASTR 100

J5-01 MAGNETIC FIELD OF A BAR MAGNET

J5-01

Visualize the magnetic field around a bar magnet

A bar magnet is positioned beneath a plastic box on an overhead projector. Sprinkle iron filings into the box above the magnet and tap the box slightly so that the filings will align along the magnetic field lines.

J5a, J5b
J5-04: MAGNETS

J5-04

Show various magnets

A varied collection of magnets is presented, including bar magnets, horseshoe magnets, disc magnets, ring magnets, and rare earth magnets. Ask about other types of magnets.

J5
J6-03: ELECTROMAGNET WITH JUNK - WITHOUT CORE

J6-03

Demonstrate electromagnetism.

This shows the functioning of J6-02 without the iron core. The absence of a core makes the field weaker, but the physics a bit simpler.

J6, PS1
K8-01 ELECTROMAGNETIC WAVE - MODEL

K8-01

Shows the relationship between the electric and magnetic field vectors in a plane-polarized traveling electromagnetic wave

Red pegs represent the electric field vector and blue pegs represent the magnetic vector. The spatial relationship between these vectors and the direction of propagation can be seen. By moving the model along its axis the temporal aspect of the wave can be shown. This wave has a wavelength of 0.81 meters, and as an EM wave would have a frequency of 370MHz

FS1
K8-51: MICROWAVE OVEN

K8-51

Demonstrate operation and experimentation with a microwave oven.

A microwave oven is provided along with a number of accessories to carry out a variety of demonstration experiments. Some of the things that you can do include: (1) Use the small neon sensors to try to see the standing wave patterns of the microwaves in the oven, (2) Make a light bulb glow by turning on the oven, (3) Create artificial lightning discharges with a candle, (4) Make sparks with a CD. DANGER: If you heat water, be aware that it can become superheated, and explode after it is removed from the oven. Use caution in heating water.

OS9
L4-06 REFRACTION IN CLOUDY WATER

L4-06

Demonstrates a light ray bends when it enters a different medium at an oblique angle.

The ray from the laser refracts when entering the surface of the cloudy water. The path of the laser beam in the water may be rendered more visible by adding a touch of powdered creamer to the water.
L7-16: GALILEOSCOPE

l7-16

Demonstrate optics of a telescope

The Galileoscope is a refracting telescope, or refractor: a long tube with a big lens (the objective) at the front end and a small lens (the eyepiece) at the back end. Light is refracted when it goes through the big lens, and then reach the eyes through the eyepiece. The scope can be disassembled to see the lenses.
M1-01: LASER DIFFRACTION - FIXED SINGLE SLIT

M1-01

Demonstrate single slit diffraction.

Position single slit in holder on cross-carriage in laser beam to obtain diffraction. Pattern can be shown on a distant screen, or the small screen shown in the picture. Magnification with the cylindrical lens can be used as necessary. One slide with four slits is available: 0.2mm, 0.04mm, 0.08mm, and 0.16mm, as well as individual slides of 0.12mm, 0.25mm, and 0.5mm.

FS1
N1-01: PRISMATIC SPECTRUM OF WHITE LIGHT - POINT SOURCE

N1-01

Demonstrate continuous spectrum

This is a convenient setup for showing the visible spectrum. A bright point source is used to provide a continuous white light spectrum. Light from the point source is focused first by an integral condenser lens and iris and then a 20cm focal length convex cylindrical lens onto an adjustable slit. A 20cm focal length convex spherical lens then images the slit through an equilateral flint glass prism onto a screen. For mechanical drawings of the original point source, see lecdem.physics.umd.edu/images/Demos/point%20source%20plans.pdf

FS1, LS1, OM1
N1-02: PRISMATIC SPECTRUM OF WHITE LIGHT - INCANDESCENT

N1-02

Demonstrate continuous spectrum

An incandescent bulb source with reflector is used to provide a continuous white light spectrum.
N1-05 SPECTRA - VISIBLE AND INVISIBLE

N1-05

Demonstrates continuous spectrum

The carbon arc lamp is used to provide a continuous white light spectrum. Light from the arc lamp is focused by a condenser lens with iris and a 20 cm focal length cylindrical lens onto a slit. A 20 cm focal length convex lens then images the slit onto the screen through an equilateral prism. A fluorescent screen (with fluorescein) is used to show that there is ultraviolet radiation, including a strong UV line, in the carbon arc spectrum. A thermopile is used to sense infrared radiation, where the heat measured by the thermopile causes an audio oscillator to rise in pitch, so a hotter source produces a higher tone. (see I2-06 for more on this apparatus) Aiming the thermopile from the spectrum back toward the prism, it is observed that the hottest part of the spectrum is just off the red color, in the infrared.

N1, OM1, LS1
N1-07: VARIATION OF SPECTRUM WITH LAMP INTENSITY

N1-07

Demonstrate continuous spectrum as the brightness of the source changes

A bright white light source is directed through a series of lenses and a prism to provide a continuous white light spectrum. The intensity of the source bulb is adjusted using a variable transformer on the input to the light source.
Engagement Suggestion
• Encourage students to predict how changing the input power will change the spectrum. Will the spectrum grow uniformly brighter and dimmer, or will there be a change in what colors we see in what proportions?

Background
As the light intensity is decreased, the spectrum becomes less intense but also shifts significantly toward the red. Increasing the source intensity, and thus the blackbody temperature, shifts the spectrum to the blue as the intensity increases.

OM1, LS1, PS1, FS0
N2-02: DIFFRACTION SPECTRA - THREE SOURCES - EXPENDABLE GRATINGS

N2-02

Demonstrate diffraction spectrum of white light along with line spectra of mercury and cadmium.

Three sources are permanently mounted on a roll-around cart, from top to bottom: (1)a clear glass long-filament incandescent light bulb which produces a continuous white light spectrum, (2) a mercury lamp which produces a line spectrum, and (3) a cadmium lamp which produces a line spectrum

These spectra are seen using 1"x2" sections of a large roll of replica diffraction grating material with 13,200 lines per inch. The pieces of grating material are relatively cheap, and may be given to the students. Tell your students to go away and look at the spectra of various lights.

The three lamps are mounted in a vertical line so the colors of the lines are the same as those in the adjacent white light spectrum. Point out that the spectra of mercury and cadmium are very different, and generalize that observation to suggest uniqueness of the spectra for each material.

N2, OS3
N2-05 DIFFRACTION SPECTRA - MISCELLANEOUS TUBES

N2-05

Shows several atomic and molecular line spectra

Use hand-held diffraction gratings to show a number of line spectra. Many of these tubes are rather weak, so this one works best for smaller groups where observers can get close to the light. Sources, which must be inserted and removed as needed by the instructor, include: hydrogen, helium, neon, argon, xenon, mercury vapor, iodine, chlorine, and oxygen (atomic spectra), carbon dioxide, water vapor, and air (molecular spectra).

N2
N2-21: PRISMATIC SPECTRUM OF MERCURY - SUPERPRESSURE LAMP

N2-21

Show a line spectrum with superposed continuum.

This is a very bright spectral source which shows bright lines as well as a continuous spectrum. Light from the superpressure mercury source passes through a condenser lens and iris and is focused onto a slit by a 10 cm focal length cylindrical convex lens. A 20 cm focal length spherical convex lens focuses the slit onto a distant screen, with the flint glass prism placed in the light just after the lens. Note that the two violet rays at the left of the spectrum are actually ultraviolet, but can be seen because of fluorescent materials in the white paper used as the photography backdrop.

DO NOT REMOVE the condenser lens, because of possible UV radiation hazard.
N2-32: ABSORPTION SPECTRA OF GLASS

N2-32

Demonstrate absorption spectrum of glass doped with various chemicals.

A bright point source with condenser lens and iris is focused by a 10 cm focal length cylindrical convex lens onto a slit, which is in turn focused onto a distant screen by a 20 cm focal length spherical convex lens. A white light spectrum is obtained by inserting an equilateral prism just after the spherical lens. A sample of glass doped with a chemical is placed in the beam just before the slit. The system now shows the absorption spectrum of the glass.

The glass selections available are neophane glass (left), holmium oxide glass (left center), and dydimium glass (right center). The spectrum of white light, without any absorbing glass, is shown at the right.
N3-02 ADDITIVE COLOR MIXING - PROJECTORS

N3-02

Demonstrates additive color mixing of light

Three slide projectors in a special three-projector mount on a roll-around cart are equipped with color filters. The projectors have been re-wired so that the intensity is adjustable by changing the voltage on the bulb without affecting the fan. The colors are easily seen, and additive color mixing can be nicely shown: R+B=M, R+G=Y, B+G=C, M+G=W, Y+B=W, and C+R=W, where R=red, G=green, B=blue, M=magenta, Y=yellow, C=cyan, and W=white.
N3-22: SUBTRACTIVE FILTERS AND THEIR SPECTRA

N3-22

Compare colors and spectra of negative filters.

Using the spectrum setup of demonstration N1-01: PRISMATIC SPECTRUM OF WHITE LIGHT - POINT SOURCE, negative color filters are positioned in the spectrum setup just before the slit to see the spectrum of light passing through the negative filters. Placing an identical filter on an overhead projector baffle allows us to view the color of the filter and its spectrum simultaneously.
Negative filters attain their color by removing the complementary color from white light.
O2-22: STROBOSCOPE AND FALLING WATER

O2-22

Demonstrate how a stroboscope works, and illustrate persistence of vision.

A water container with a nipple near the bottom is connected to a plastic tube and eye dropper to produce a stream of water which breaks up into a series of water droplets. The water stream is illuminated by a stroboscope and viewed by a TV camera. Adjustment of the strobe frequency can make the water droplets move up or down either slowly or rapidly, or even stand still!

O2, LS1
O3-21: BENHAM TOP

O3-21

Demonstrate perception of color due to periodic excitation of the eye.

A disc contains half black and half white fields with various sets of azimuthal black lines on the white field. Rotating the disc a few times per second creates circles which appear to have various mild coloration, from greens to browns to blues. Rotating in the opposite direction changes the colors.