4.5 Electromagnetic Induction

Question 1

What is Faraday’s law?

Answer 1

The magnitude of the inducted emf is directly proportional to the rate of change of magnetic flux linkage.

Question 2

What is Lenz’s law?

Answer 2

The direction of the induced emf (or current ) is always such that it opposes the change that caused it.

Question 3

What can be used to find the direction of induced current?

Answer 3

Fleming’s Right-hand rule.
Thumb = Motion (or force)(F)
First finger = Field (B)
Middle finger = Induced current

Lenz’s law means the current (middle finger) points in the opposite direction so the right hand it used.

Question 4

What is magnetic flux and its formula?

Answer 4

The number of field lines passing a given area, ϕ

ϕ = ABcos(θ)

A = Area of surface (e.g. coil plane)
B = Magnetic flux density
θ = The angle between normal of area surface and the field

Question 5

What is the formula for induced emf?

Answer 5

V = - ΔNϕ/Δt
or
V = -ΔBANcos(θ)/Δt

N = number of loop (or turns) in the coil.
The negative sign is due to Lenz’s law

Question 6

What is flux linkage?

Answer 6

Flux linkage = Nϕ = BANcos(θ)
N = number of turns (or loops) in a coil.
It’s the magnetic flux for a coil basically.

Question 7

What are the two common ways of inducing an emf?

Answer 7

1) Changing area over time
2) Changing flux density over time

Question 8

What’s the formula for inducted emf of a wire sliding along a conducting track in a magnetic field?

Answer 8

V = -ΔBAN/Δt

Area increases at: lvΔt

V = BlvΔt/Δt = Blv

V = Blv