Electricity and Magnetism - SS2 Physics Past Questions and Answers - page 5
Faraday's law of electromagnetic induction states that the magnitude of the induced EMF is proportional to:
The number of turns in the coil
The cross-sectional area of the coil
The time the magnetic field is present
The angle between the magnetic field and the coil
Lenz's law is a consequence of Faraday's law and states that the induced current in a conductor always flows in a direction that:
Enhances the original magnetic field
Opposes the original magnetic field
Is perpendicular to the original magnetic field
Does not depend on the original magnetic field
A magnetic field is changing at a rate of 0.2 T/s. If the number of turns in a coil is 100 and the area of the coil is 0.05 m², what is the magnitude of the induced EMF in the coil?
The induced EMF can be calculated using the formula: EMF = -N x (ΔΦ/Δt), where N is the number of turns and ΔΦ/Δt is the rate of change of magnetic flux.
Given: N = 100 turns, ΔΦ/Δt = 0.2 T/s, A = 0.05 m²
Substituting the values into the formula:
EMF = -100 x (0.2 T/s) = -20 V
The magnitude of the induced EMF in the coil is 20 V.
A circular loop of radius 0.1 m is placed in a uniform magnetic field of 0.5 T. If the loop is rotated from a position where the magnetic field lines are perpendicular to the plane of the loop to a position where the magnetic field lines are parallel to the plane of the loop in 0.2 s, what is the average induced EMF in the loop?
The average induced EMF can be calculated using the formula: EMF = -N x (ΔΦ/Δt), where N is the number of turns and ΔΦ/Δt is the average rate of change of magnetic flux.
Given: N = 1 (single loop),
ΔΦ/Δt = (Φ₂ - Φ₁) / Δt = (B₂A - B₁A) / Δt,
B₁ = 0.5 T,
B₂ = 0 T,
A = πr²,
r = 0.1 m,
Δt = 0.2 s
Substituting the values into the formula:
EMF = -1 x ((0 - 0.5 T) x π x (0.1 m)²) / 0.2 s
= -1 x (-0.0157 V)
= 0.0157 V
The average induced EMF in the loop is 0.0157 V.