25_EM_Induction_and_Waves

# 25_EM_Induction_and_Waves - Magnetic forces review Please...

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1 Magnetic forces review Please try chapter 24 problem 39 on page 827. “A square current loop 5.0cm on each side carries…”

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2 Electromagnetic Induction and Waves EM induction of electric currents Effects of moving conductors in B fields Effects of conductors in changing B fields Eddies Electromagnetic Waves Polarization, Photons Electromagnetic spectrum
3 EM induction and waves • EM Induction – making currents from changing magnet fields • EM waves – radio, microwaves, light, X-rays

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4 Induced Current • We have seen that a magnetic field exerts a force on a moving charge or current • Faraday found that a changing magnetic field will move a charge, inducing a current
5 Induced Current • A changing magnetic field creates an induced current in a circuit. • The process is called electromagnetic induction

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6 Motional emf • A conductor moving in a magnetic field experiences a changing magnetic field • The charge moves in the conductor, creating an electric field
7 Motional emf • If the wire is moving at velocity, v, the charges move, until the forces from the electric field (E), and magnetic field (B) balance. vB E qE F qvB F E B

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8 Motional emf • The motional emf across the wire length l, moving in a magnetic field, B, at velocity v, is found from vlB V vB E l V E emf emf
9 Energy of induced currents Consider a conductor moving along rails in a magnetic field We now have a current loop, and given the resistance, R, can calculate the current R vlB R V I emf

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10 Energy of induced currents The force on the wire can be found from R B vl F l R vlB B BIl F wire wire 2 2
11 Energy of induced currents We can substitute for the power needed to drag the wire, and the power dissipated by electrical resistance R B l v R I P R B l v v F P output wire input 2 2 2 2 2 2 2

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25_EM_Induction_and_Waves - Magnetic forces review Please...

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