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Electromagnetic Induction by Mind Map: Electromagnetic Induction
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Electromagnetic Induction

N = number of turns in coil

A = area of surface


where f = 1 / T

T = Period of revolution

AC Generator

Φ = NBAcosθ, BUT, θ = ωt, Hence, Φ = NBAcos ωt

Eddy Currents

Magnetic Effect, can be reduced by creating slots in the plate, Eddy currents cannot pass through air gaps, Follow Lenz Law, oppose the motion producing them

Heating Effect, coil carrying high frequency ac, causes rapidly changing magnetic flux to induce large eddy currents

Φ = Nϕ



Product of the magnetic flux density & the area normal to the field through which the field is passing

∆Q = ∆Φ / R

Unit: Wb (Weber)

Φ = BAcosθ

induced emf as B parallel plane of disc and axis of rotation


copper disc rotates at frequency f between poles of magnet

Units of E: V (Volts of induced current)


l = length of conductor

Index - Magnetic Field Direction

The induced emf, E, in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit

Direction of induced emf is such that it tends to oppose the flux-change causing it, and does oppose it if induced current flows


θ = angle between the magnetic field and the surface S


Magnetic flux ϕ

Magnetic flux linkage Φ

Total flux through the coil

Unit: Wb (Weber)

Φ = NBAcosθ

Q = NBA / R

R = total resistance of circuit

Faraday's Law

E <>< d/dt x (Nϕ)

Middle Finger - Induced Current Direction



Lenz's Law

E = - dϕ / dt

E = - N d(BAcosθ) / dt

Unit: V (Volts)

If this were not the case, magnet's velocity and KE would be increased indefinitely, but there is no source for the energy, so COE is violated

derived from Conservation of Energy

Fleming's Right Hand Rule

Thumb - Force Direction

B = magnetic flux density

Currents that are caused in metals moving in a magnetic field

can be +ve or -ve

EMF induced in Moving Straight Conductor

E = Blv

v = velocity

E = 0, when l or v is parallel to B

Applications of EMI

Use of search coil to measure flux density

Use of search coil to measure B

Disc Generator

E = Bπr²f

N pole induced in top of solenoid when magnet's North is moved towards solenoid to oppose direction of magnet

Use Right hand grip rule to determine direction of current

Note: If l or v is not perpendicular to the field lines

Component perpendicular to the field should be used