lecdem.physics.umd.edu - Needs New Photo

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E2-49: PULSAR MODEL - RADIOWAVES

E2-49

Show the changing field pattern from a rotating dipole.

Position antenna so that the electric field from the transmitter picked up by the receiving antenna lights the lamp on the antenna. Then rotate the transmitting antenna with its stand, causing the light to turn on and off, dependent on the dipole radiation pattern of the antenna.
E2-50: PULSAR MODEL - FLASHLIGHTS

E2-50

Illustrate beaming pattern of pulsars and pulsed binary X-ray sources.

Flashlights are mounted antiparallel to each other on a rod which is mounted at an oblique angle onto a second rod. The second rod is then rotated to obtain the pulsar effect. The angle of obliquity can be easily adjusted.

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E2-54: REFLECTING TELESCOPE - STRING MODEL

E2-54

Shows how rays are focused by a standard reflecting telescope.

Parallel rays incoming from a star at infinity (red strings) are focused by the large mirror to a focus near the aperture of the telescope. The reflected rays (white strings) are intercepted before their focus by a small mirror, and deflected upwards toward the eyepiece of the telescope. The eyepiece is positioned at its focal distance past the focal plane of the objective (mirror).
E2-61: GALAXY MODEL

E2-61

Illustrate our galaxy.

This is a model of our galaxy, the size of the milky way shrunk to about 50cm diameter, a ratio of 1:2x10⁺²¹!! See table of interesting sizes in the Demonstration Reference File, a copy of which is available with the demonstration.

The red marble locates the approximate position of the solar system.

FRAGILE! Be careful.

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E2-71: MILLISECOND PULSAR

E2-71

To "hear" the signal from a pulsar.

This audio tape cassette contains the signal from a pulsar converted to audio frequencies.
Note: requires large audio cart to play in lecture halls.

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E2-72: AUDIOTAPE 14 MIN - NRAO PULSAR

e2-72

To listen to a pulsar

This audio cassette tape contains 14 minutes of pulsar signals converted to audio. Obtained through the NRAO.
Note: requires large audio cart in lecture halls.

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E2-73: AUDIOTAPE 18 MIN - SOUNDS FROM SPACE

E2-73

Tape of signals from several early artificial satellites.

Some of the most significant scientific events leading to the launching of the Echo I satellite on August 12, 1960 are described here. Excerpts from messages received from previous artificial satellites in space are presented, including Sputnik, Explorer, and the Vanguard series. Project Echo sounds are also played, with accompanying narration.
Note: Requires large audio cart in lecture halls.

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F1-02: FLUID PRESSURE VS DEPTH - ANEROID GAUGE

F1-02

Show water pressure versus depth with an aneroid gauge.

An L-shaped glass tube, connected to an aneroid gauge, is immersed in water. The pressure at any depth is indicated directly on the gauge. This enables students to see the pressure at any level.
Invite students to make predictions about the relationship between depth and pressure, and perhaps even sketch what they expect the graph of this relationship to look like. Then take a few data points and see what happens.

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F1-03: PASCAL'S VASES

F1-03

Demonstrate that pressure is dependent only on depth, and not on the shape of the container.

Three "vases" with different shapes can be connected to a water reservoir and pressure gauge assembly. Using the wire as a depth indicator, it is shown that the pressure in the vase depends only on the depth, not on the shape of the vase.
F1-04: EQUILIBRIUM TUBES

F1-04

Demonstrate that pressure is transmitted equally throughout a fluid.

By raising and lowering the reservoir, one can show that the water level in all three vases will rise and fall together. From this one concludes that pressure is transmitted uniformly throughout the water.

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F1-05: DOES WATER SEEK ITS OWN LEVEL?

F1-05

A trick to challenge the students.

The liquid level in the left side of the U-tube is higher than that in the right side of the U-tube. How does one explain this?

Two immiscible fluids of different density which are identical in physical appearance are in the two ends of the U-tube. The point where they meet (which could be easily seen) is covered by the clamp which holds the U-tube.
F1-12: PASCAL'S LAW - COILED TUBE PARADOX

F1-12

Illustrate Pascal's law in a dramatic way.

Referring to the photograph on the right, pouring water (colored green) into the tube at the left in the photograph causes the asymmetric configuration shown due to the equalization of pressure in the central air bubble. Similarly, if one end of a three-turn loop of tubing is raised vertically, as in the photograph at the left above, water poured into the high end will never come out the bottom end, even when the bottom end is lying flat on the table, as seen in the left photograph.
F1-13: CONSTANT WATER PRESSURE

F1-13

Demonstrate a mechanism which produces a constant water pressure.

Air enters the aspirator bottle, initially almost filled with water, through a tube inserted through a sealed stopper into the water bath, while the water leaves through a nipple near the bottom of the bottle. This arrangement provides a constant water pressure head, which is equal to the height of the water column between the nipple and the bottom end of the tube. Thus the water jet will have the same range as the water level in the bottle falls from its initial level to the level of the bottom of the tube.

The idea of this gizmo to provide water at a constant pressure, was first proposed by Edme Mariotte, a 17th century French scientist. A device called the Mariotte siphon, making use of this concept, is used in agriculture to provide irrigation at a constant flow rate and as a research tool in determining the properties of soil. His work is also cited in the Catholic Encyclopedia.
F1-14: PISTON DIAMETER VS TRAVEL - WORKING MODEL

F1-14

Show that with an incompressible fluid the bigger piston moves more slowly than the smaller piston.

Raise or lower one of the bottles to observe the relative speeds of the changing water levels. This is what happens in a confined incompressible fluid with pistons on the two water surfaces.
F1-15: PRESSURE GLOBE

F1-15

To illustrate several interesting phenomena related to air pressure

This is a glass sphere into which a balloon can be inserted to demonstrate effects of air pressure. The sphere can be sealed with a rubber stopper. Three ways to use the Pressure Globe:
(1) Place a balloon into the lipped opening of the Pressure Globe. After stretching the mouth of the balloon over the lip, blow into the balloon until it conforms to the bottle's interior surface. Insert the stopper in the bottom hole while retaining the pressure inside the balloon. Once the stopper has been firmly inserted, remove your mouth from the balloon. Observe that the balloon does not deflate.

(2) Place the balloon into the lipped opening of the Pressure Globe and place the stopper in the bottom hole. After stretching the balloon over the lip, have a student blow into the balloon. Air cannot be blown in. Discuss why not.

(3) Prepare the Pressure Globe following the procedure in Step 1. Once the balloon has been fully inflated and the stopper placed in the bottom hole, pour approximately 100 ml of water into the balloon. With the large opening facing upward, place the Pressure Globe over a sink. Now remove the stopper. Observe what happens. Discuss what force causes the water to squirt out of the bottle.

Note: Care must be taken to insert the rubber stopper far enough that it fully seals, but not so far that it cannot be grasped to be removed.
F1-21: LIPLESS STRAW

F1-21

Demonstrate the role of atmospheric pressure in the operation of a drinking straw.

The initial configuration of the water in the bottles is seen in the photograph at the left above. When air is pumped out of the bell jar, water flows through the tube from the stoppered bottle into the open bottle, as seen in the photograph at the right. When air is allowed to flow back into the bell jar, the water flows back into the closed bottle, reproducing the initial water configuration.
F2-03: CARTESIAN DIVER - EXPLICIT VERSION

F2-03

Demonstrate explicitly how a cartesian diver works by showing how the water enters the diver when the pressure in the cylinder is increased.

When no additional pressure (above normal atmospheric pressure) is applied to the membrane on top of the cylinder, the diver floats at the surface of the water. The location of the water surface inside the diver is indicated by the orange bob floating in the diver tube. When additional force is applied to the membrane the pressure in the tube increases, forcing more water into the diver tube and compressing the air in the tube, as indicated by the bob. Because the average density of the diver becomes greater than that of water, the diver sinks to the bottom. When the force is released, the diver again rises.
F2-04: BUOYANCY - SPHERE AND WATER

F2-04

Challenge the students' thinking about the buoyant force by considering the question: "Will a round object, without a flat top and bottom surface, experience a buoyant force, as does a cylinder?"

A round steel ball and a hollow metal can hang from the scale. The pressure is always normal to the surface of a body and increases linearly as the depth increases. When the steel ball is immersed it too experiences a buoyant force, because the upward vertical component of pressure applied to the lower hemisphere is greater in magnitude than the downward vertical component of the pressure exerted on the upper hemisphere.
F2-10: BUOYANT BUBBLES

F2-10

Demonstrate buoyancy and diffusion in an interesting way.

A block of dry ice is placed in the bottom of a clear plastic cylinder sealed on the bottom, trapping carbon dioxide in the bottom of the container as the dry ice sublimates (evaporates). Bubbles produced with a standard soap bubble blowing gizmo will float on top of the more dense carbon dioxide. Some carbon dioxide diffuses into the bubbles, so they get larger and sink! Some of the bubbles freeze when they sink to the bottom of the container near the dry ice. The photograph at the right is a detail of the top of the container.

It may be necessary to remove static electricity from the plastic container. A damp cloth or lit match may assist with this.
F2-11: HYDROMETER

F2-11

Measure the density of a liquid.

If the hydrometer is immersed in a graduated cylinder filled with water, the reading on the scale (center photograph) should be C(W) = 1000, indicating that the scale is calibrated for water. If the hydrometer is put into the saline solution (photograph at right), the number C(L) at the level of the liquid is read. The density D(L) of the unknown liquid is given by: D(L)=C(L)*D(W)/1000,where D(W) is the density of water in kg/m^3. One can measure densities between 0.7 and 2.0 using this device.

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