Concepts

Electricity, force on moving charge, right hand rule

Overview

A beam of electrons is deflected by a magnet and/or charged plates.

Details

Equipment

• [1] Cathode ray tube (Crookes tube)
  
• [1] Crookes tube power supply or [1] Heathkit IP-32 power supply with (optional) [1] Xantrex XT 60-1 power supply
• [6] Banana cable
• [1] Bar magnet
• [1] Stack of rare earth magnets
  
• [1] Power bar with long cord
• [1] Black sheet of paper
  
• [1] Camera (lecture hall document camera should be fine)
  

Classroom Assembly

1. Dim lights in order to make the electron beam more visible.
2. Wire up the heater and accelerator contacts (and also deflector contacts, if desired) on the tube to the power supply (or supplies).
3. If using the Heathkit supply, let it warm up by leaving it on standby for a few minutes.
4. If using an external camera, position and focus it to see the tube end-on. Leave the camera on.
5. Turn off automatic brightness adjustments on the camera, if applicable.
   

Important Notes

• Be careful not to get shocked by the high voltage terminal.
• Do not exceed 300 V on the accelerating voltage from the Heathkit power supply.
• A common error is to use the left-side knob on the Heathkit supply.

Script

1. Project the camera view to the class.
2. Dim the lights.
3. Turn on the power supply or supplies.
4. Increase the accelerating voltage.
   
5. Deflect electrons using magnet.
6. Make the electrons curl around magnetic field lines by positioning the rare earth magnets where the beam hits the tube.
   
7. (Optional) Deflect electrons with the deflector plates.
   
8. When done, turn down all voltages.
9. Turn off the power supply or supplies.

Additional Resources