Electromagnetic Induction

Group: InductionWong Chun JieLeong Qi Dong

Jwa Li Wen4S2

2012 T3

Introduction

• Current flowing through a conductor produces a magnetic field

• Can a magnetic field produce a current in a conductor?

Video

• http://www.youtube.com/watch?v=ITuR3AQAYI8

• 1:07:50 – 1:10:4`

Theory – Electromotive Force (emf)

A varying magnetic flux produced an e.m.f, which produces an induced current in a closed circuit.

Faraday’s Solenoid Experiment

Steps

1. Move magnet into solenoid2. Leave the magnet in solenoid3. Move magnet out of solenoid

VariablesDependent:(1) Deflection of galvanometer pointer (2) Direction of deflection(3) Magnitude of deflection

Independent:• Pole of magnet• Number of turns in solenoid• Strength of magnet• Cross-sectional area of solenoid• Speed of magnet being moved in and out

Results

(1) Deflection of galvanometer pointer

• Deflects: magnet is moving in and out of solenoid

• Does not deflect: magnet remains stationary in solenoid

• Current is flowing through circuit only when the magnet is moving in and out of the solenoid

Conclusion

• A varying magnetic field produces an e.m.f, which produces an induced current in a closed circuit.

Results

(2) Direction of deflection

Action of Bar Magnet

Direction of Deflection

Direction of e.m.f

N-pole inserted Right Anti-clockwiseN-pole withdrawn Left ClockwiseS-pole inserted Left ClockwiseS-pole withdrawn Right Anti-clockwise

ConclusionLenz’s Law• The direction of the induced emf, and thus,

the induced current in a closed circuit, is always such that the magnetic effect always opposes the change producing it.

• Why oppose?– In Work, Energy, Power: GPE = KE– In Electromagnetic Induction: GPE = KE + Electrical

energy– KE decreases for the conservation of energy

Results

(3) Magnitude of deflection

Increase in • number of turns in solenoid • strength of magnet• cross-sectional area of solenoid• speed of magnet being moved in and out Increases deflection – increases emf

N

ΦB

Rate

Conclusion

• Faraday’s Law of Induction• Where ℰ is the emf

• Induced emf generated in a conductor is proportional to the rate of change of magnetic flux vector linking the circuit.

References

• http://physics.tutorvista.com/electricity-and-magnetism.html#close_iframe

• http://en.wikipedia.org/wiki/Faraday's_law_of_induction

• http://en.wikipedia.org/wiki/Magnetic_flux• http://en.wikipedia.org/wiki/Electromotive_fo

rce

Thank You