Magnetic Force on an Electron Beam (Using e/m Apparatus)

The setup demonstrates the force of a magnetic field on moving electric charges. It consists of pair of Helmholtz coils surrounding a vacuum tube filled with an inert gas. As current passes through the coils, a uniform magnetic field is created between them. The vacuum tube contains an electron gun that produces a glowing beam as the gas atoms are excited by the moving electrons. As the current in the coils is increased, the beam is bent into a circle from the force of the magnetic field. A bar magnet can be used to further deflect the beam.

* Equipment seen in the video may vary from equipment used in ND Demonstrations. See information and images below for ND equipment and setup.

Setup:

Connect the equipment as shown in the photo. The e/m apparatus should be located in the middle of the lab table with the Tenma power supply to the left and the Pasco power supply to the right (when looking at the front of the equipment). Connect the " - " terminal on the Tenma power supply with a black banana cable to the black banana jack for the Helmholtz Coils (located one the left side of the e/m apparatus). Connect the " + " terminal of the Tenma power supply to the red banana jack for the Helmholtz Coils using a red banana cable. Using two black banana cables, connect the yellow jacks on the Pasco power supply to the black terminals for the heater (located on the far right side of the e/m apparatus; orientation does not matter). Using a red banana cable, connect the High Voltage red terminal on the Pasco power supply to the red terminal for the electrodes (second column in on the right side of the e/m apparatus). Use the last black banana cable to connect the black terminal for " + 500 V " on the Pasco power supply to the black terminal for the electrodes.

Ensure the equipment is properly connected before turning it on. Turn the knobs on the supplies down so that everything is at zero to begin. Turn off the lights in the room.

Turn on the power supplies. The Pasco power supply should be set at approximately 200-220 V for the electrodes. It may take a moment for a blue-green beam to be visible. Turn up the voltage on the Tenma power supply for the Helmholtz Coils to see the beam deflect into a circle.

Notes:

CAUTION: High Voltage. Ensure that equipment is setup properly before use!

Should be performed in a darkened room in order to see the electron beam.

Instructors can use a bar magnet to further deflect the electron beam.

Courses Used In:

• PHY 10320

• PHY 20435

• PHY 30220

Discussion and Polling Questions:

Coming Soon

Equipment Needed:

• Tenma 0-18V DC Power Supply

• Pasco SF-9585A High Voltage Power Supply

• e/m Apparatus

• 2 Red Banana Cables

• 4 Black Banana Cables

• 1 Power Cable

• Bar Magnet (optional)