Physics

Problem

A coil of

200

turns and area

0.05\,\text{m}^2

is initially with its plane perpendicular to a

0.30\,\text{T}

uniform magnetic field. It is rotated through

90^{\circ}

at constant speed in

0.010\,\text{s}

and is connected to an external resistance of

5\,\Omega

. Neglect the coil’s own resistance. The total charge that flows through the resistor during the rotation is a)

1.20\,\text{C}

3.00\,\text{C}

0.60\,\text{C}

0.30\,\text{C}

Intuitive explanation

This problem hinges on Faraday's law of electromagnetic induction and the relationship between charge flow and total magnetic flux change—not the induced EMF itself. When the coil rotates, the magnetic flux through it changes from maximum to zero, and that total change in flux determines how much charge flows, independent of how fast the rotation happens. The key insight is that charge depends only on $\Delta \Phi = NBA\Delta(\cos\theta)$ and resistance, so you can find the answer without worrying about the time interval or instantaneous EMF.

Intuitive explanation

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