5J10.20 Back-EMF: Light Bulb
Concepts
Inductor back-EMF, Faraday's law, Lenz' law
Overview
When external current to an inductor is suddenly cut off, the inductor responds by temporarily producing a large EMF that can light a light bulb. In this way, a 6 V battery can momentarily illuminate a 120 V light bulb.
Details
Equipment
- [1] Large inductor (~0.5 H)
- [1] 40 W light bulb with socket
- [1] 6 V battery
- [1] SPST switch
- [5] Banana cable
- [4] Insulated alligator clip
Classroom Assembly
- Make sure switch is in the open position.
- Hook up banana cables.
Important Notes
- The inductor is very heavy. Be careful when lifting it.
- Do not short-circuit the battery for a long time.
Script
- Dim the room lights.
- Close the switch for about 2 seconds.
- Open the switch.
- Brighten the room lights.
Additional Resources
References
- PIRA 5J10.20
Disclaimer
- Don't attempt this at home!
Last revised
- 2022
Technicals
- The inductor is labelled as 0.5 H and 1.5 Ω
- Direct connections between the light bulb and inductor seem to work best, instead of connections that take intermediate routes through terminals on the switch or battery
- Resistance of the battery and light bulb seem to be important
Related AV
Related demos
- Permanent magnet induction
- Solenoid induction with a battery
- AC induction
If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.