A circular coil of radius R=10 cm having 500 turns and total resistanc...
A circular coil of radius R=10 cm having 500 turns and total resistanc...
Explanation:
The induced emf in a coil is given by Faraday's Law as follows:
emf = -N(dΦ/dt)
where N is the number of turns in the coil and Φ is the magnetic flux through the coil.
Finding magnetic flux:
The magnetic flux through the coil can be calculated as follows:
Φ = B.A.cosθ
where B is the magnetic field strength, A is the area of the coil, and θ is the angle between the normal to the coil and the magnetic field.
Given that the coil is initially perpendicular to the magnetic field, θ = 90°. Therefore, cosθ = 0.
Φ = B.A.0 = 0
This means that there is no magnetic flux through the coil initially.
Finding the induced emf:
When the coil is rotated by an angle of π in 0.5 seconds, the magnetic flux through the coil changes. The new magnetic flux through the coil can be calculated as follows:
Φ = B.A.cosθ
where θ is the angle between the normal to the coil and the magnetic field.
When the coil is rotated by an angle of π, θ changes from 90° to 270°. Therefore, cosθ changes from 0 to -1.
Φ = B.A.(-1) = -B.A
The change in magnetic flux is given by:
ΔΦ = Φf - Φi = -B.A - 0 = -B.A
The time taken for the coil to rotate by an angle of π is 0.5 seconds. Therefore, the average rate of change of magnetic flux is:
(dΦ/dt) = ΔΦ/Δt = (-B.A)/0.5 = -2B.A
The induced emf in the coil is therefore:
emf = -N(dΦ/dt) = 500(-2B.A) = -1000B.A
The negative sign indicates that the induced current will flow in a direction to oppose the change in magnetic flux.
Finding the induced current:
The resistance of the coil is given as 2 ohms. Therefore, the induced current in the coil is:
I = emf/R = (-1000B.A)/2 = -500B.A
The negative sign indicates that the induced current will flow in a direction opposite to the direction of the initial current.
Substituting the given values, we get:
B = 3×10^-5 T
A = πR^2 = π(0.1)^2 = 0.0314 m^2
Therefore,
I = -500(3×10^-5)(0.0314) = -0.047 mA
Since the answer cannot be negative, we take the magnitude of the answer as follows:
I = 0.047 mA
Therefore, the induced current in the coil is 0.047 mA, which is closest to option (b) 1.0 mA.
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