Electromagnetic Induction Flashcards
Define magnetic flux.
The product of flux density and area normal to the flux.
Formula for magnetic flux.
Φ = BA
Unit of magnetic flux.
weber
Wb
Define the weber.
The magnetic flux with flux density of 1 T passing through an area of 1 m^2 normal to the field.
Define magnetic flux linkage.
The product of the number of turns and the magnetic flux.
Formula for magnetic flux linkage.
magnetic flux linkage = NΦ = NBA.
An e.m.f. can be induced by a changing magnetic flux. This effect is called ______ .
electromagnetic induction.
State Faraday’s law of electromagnetic induction.
The induced e.m.f. is proportional to the rate of change of magnetic flux linkage.
The direction of the induced e.m.f. or current in a wire moving through a magnetic field at right angles to the field may be determined using _________ rule.
Fleming’s right-hand rule.
State Lenz’s law.
The direction of the induced e.m.f. produces effects to oppose the change causing it.
Formula which combines Faraday’s law of electromagnetic induction and Lenz’s law.
E = - Δ(NΦ)/Δt = - Δ(NBA)/Δt
E = - Δ(NΦ)/Δt
What does the minus sign indicate?
Minus sign indicates that the direction of the induced e.m.f. produces effects to oppose the change causing it.
Explain how a transformer works.
In a transformer, an alternating current is supplied to the primary coil. This produces a changing magnetic field in the soft iron core. Hence, the magnetic flux linkage with the secondary coil is always changing. According to Faraday’s law, a changing e.m.f. is induced in the secondary coil.
When a metal disc spins in a magnetic field, damping occurs. Explain why.
When a metal disc spins in a magnetic field, it cuts through the magnetic flux and an e.m.f. is induced in the disc. However, because the rate of cutting of flux varies from one part of the disc to another, different regions of the disc will have different magnitudes of e.m.f. Hence, eddy currents are induced in the disc. The eddy currents cause heating in the disc and the energy of the disc is dissipated. This causes the disc to slow down.
