Columbia University Physics Lecture Demonstrations


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Mechanics
Fluid Mechanics
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Thermodynamics
Electricity and Magnetism
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5H30.21 Forces on an Electron Beam

[Setup Time: 5 Min.] [Current Condition: Good]

Info

A beam of electrons in bent in a circle by large Helmholtz coils.

Setup Instructions

1. Attach the various power supplies and meters as shown in the diagram, noting that the connection to the regulated power supply should be connected to on the high voltage setting. It is important that the voltage going to the heater does not exceed 6.3 V, as this could damage it.

2. The current can be finely adjusted by the knob on the device. eB/m = velocity/r = w, and e/m = 2 *Voltage/(B^2 * r^2), where B is the magnetic flux density, ~7.8*10^-4 T, according to the device.

3. To go back and forth between the relationships, note that eV = ½ m v^2. B at the midpoint between the coils can be determined by noting that B ~ 9.02 * 10^-7 N * I / R, where R is the average of the radius of the coils.

Parts List

e/m setup in M1B

2 HP power supplies in D2B

Multimeter in various desks/workrooms

Regulated power supply in D2B

6-8 banana plug cables in backwall

Power cables in back wall

Relevant Simulation

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Other Information

Circular E and M

Real-Life Examples

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More Advanced Reading

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