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N-pole inserted Right Anti-clockwiseN-pole withdrawn Left ClockwiseS-pole inserted Left ClockwiseS-pole withdrawn Right Anti-clockwise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