Concepts

Faraday's law, induced current, electromagnets

Overview

This is a series of interactive lecture demonstrations with a theme of induction and Faraday's law, typically presented with a series of iClicker questions. Students predict the direction of current flow (or lack thereof) during interactions between a coil and a permanent magnet, then observe the experiment. They then repeat this for interactions between a coil and a DC electromagnet.

Details

Equipment

• [1] Search coil with banana connectors
• [1] Solenoid
• [1] Galvanometer-style voltmeter
  
• [1] SPST switch
• [1] Telegraph switch
• [1] 6 V battery
• [1] Permanent magnet
• [2] Banana cable
• [2] Sheathed alligator clip
• [2] Lab stand
• [2] 90-degree clamp
• [1] 3-finger clamp
• [1] Lab jack 

Classroom Assembly

1. Mount the search coil on a lab stand using a 90-degree clamp and a 3-finger clamp.
2. Mount the permanent magnet on the other lab stand using a 90-degree clamp.
3. Connect the search coil in series with the SPST switch and voltmeter.
4. Place the solenoid on the lab stand and raise the solenoid to the level of the search coil.
5. Wire up the battery, telegraph switch, and solenoid in series with each other. Use the sheathed alligator clips to avoid shorting the battery.
6. Arrange the magnet and search coil so that from the students' point of view, the magnet is left of the coil, with north facing the right. Flip the search coil if it doesn't give the desired direction of current in induction experiments. The solenoid should be set up so that closing the telegraph switch results in a magnetic field to the right.
   

Important Notes

• Try not to short the battery for very long.

Script

1. Do experiments with the magnet and search coil, asking students to predict the direction of current flow through the switch and galvanometer. 

   Search Coil Switch	What's Moving?
   Open → closed	Nothing
   Closed	Magnet, left
   Closed	Magnet, right
   Closed	Search coil, right
   Closed	Search coil, left

2. Replace the permanent magnet with the solenoid on a lab stand. Do experiments with the solenoid and search coil, asking students to predict again the direction of current flow through the switch and galvanometer.
   

   Search Coil Switch	Solenoid Switch
   Open → closed	Closed
   Closed	Open → closed

Additional Resources