A rigid square coil with 50 turns lies in a region where the magnetic field is…

PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

A rigid square coil with 50 turns lies in a region where the magnetic field is perpendicular to the coil’s plane. Beginning at time

t=0

, the magnetic field changes according to

B(t)=0.25\,\text{T}-0.060\,\text{T\,s}^{-1}t

. Simultaneously, one side of the square is pulled outward so that the coil’s side length grows linearly from

0.12\,\text{m}

at a rate of

+1.5\times10^{-3}\,\text{m\,s}^{-1}

. Throughout the process the coil remains planar and perpendicular to the field. (a) Calculate the magnitude of the induced emf in the coil at

t=2.0\,\text{s}

. (b) Determine the induced current at that instant if the total resistance of the coil is

4.0\,\Omega

. (c) Specify whether electrical energy is being delivered to or extracted from the external agent that stretches the coil at

t=2.0\,\text{s}

, and explain.