PMDC Verified Question 40 of 69
A copper hoop is held in a vertical east-west plane in a uniform magnetic field whose field lines run along the north-south direction. The largest induced emf is produced when the hoop is?
A
Rotated about a north-south axis
B
Rotated about an east-west axis
C
Moved rapidly, without rotation, toward the east
D
Moved rapidly, without rotation, toward the south
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Rotated about an east-west axis
Concept:

Maximum EMF is induced when the rate of change of magnetic flux is maximized. This happens when the coil physically cuts through the magnetic field lines optimally.

Solution:

  • The magnetic field runs North-South. The hoop is initially in an East-West plane, meaning maximum flux is passing through it.


  • To create the greatest change in flux (cutting the lines), the hoop must flip out of this alignment. Rotating it around an East-West axis will cause its plane to repeatedly intersect the North-South field lines, inducing maximum EMF.


Why other options are incorrect:

Rotating about a North-South axis spins the hoop like a steering wheel relative to the field lines; the flux doesn't change, so zero EMF is induced. Linear motion without rotation in uniform fields does not change the flux linking the area.

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