Question

For the following situations involving a bar magnet and circular conducting loop, indicate the direction of the induced current in a diagram and explain your reasoning clearly.

(a) You move the north pole of the magnet towards the loop, keeping the magnet aligned with the symmetry axis of the loop.

(b) You move the south pole of the magnet towards the loop, keeping the magnet aligned with the symmetry axis of the loop.

(c) You move the north pole of the magnet away from the loop, keeping the magnet aligned with the symmetry axis of the loop.

(d) The north pole approaches the loop and goes through it. Hint: Does the direction of the current change or does it stay the same as the magnet goes through?

Answer 1

For a magnet, field lines are

  

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(a)

For north pole moving towards the coil, the flux through the coil is increasing , so a magnetic field is induced to oppose this change and therefore, induced current will be clockwise as seen from left

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2)

For south pole moving towards the coil, the flux through the coil is decreasing , so a magnetic field is induced to oppose this change and therefore, induced current will be counter clockwise as seen from left.

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3)

For north pole moving away, the flux into the coil is decreasing, so an induced field is set up into the coil to oppose this decrease. so, induced current will be counter clockwise.

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4) As the north pole approaches, the flux will be increasing into the loop, so induced current will be as same as part (1) then as the magnet passes through the flux starts to decrease and however, if we use right hand rule, we will see that current direction remains the same.