The figures below show two different situations where a current may be induced i

Question

The figures below show two different situations where a current may be induced in a loop by Faraday's Law, with the direction determined by Lenz' Law. The magnetic field is shown by the x's in Fig. 2. Choose true or false for each statement for the current in the loop. (The compass directions are defined in the usual way.) fig1: Loop moving East, induced current a. fig1: Loop moving East, induced current b. fig2: Loop moving East, induced current a. fig2: Loop moving West, induced current b. fig2: Loop moving South, induced current b. fig2: Loop moving North, no induced current.

Explanation / Answer

First question:

As the loop moves towards bar magnet, the number of field lines entering the loop increases. According to Lenz's law, to oppose this emf will induce in the coil such that it tries to decrease the increasing magnetic field. Only if the current flows in the downward direction, it can decrease the increasing field. So, first one is false.

Second question:

From same previous arugment it is clear that field must be downward. So, direction of current is given by b. Hence it is true.

Third Question:

As the coil moves towards east, from the figure it is clear that the field lines start to decrease. in order to oppose the change it has to induce current such that the field inside the loop increases to oppose the decrease in field. So, direction of current is given by a. It is true

Fourth question:

Using same argument, it can be shown that the field direction is given by b. So, it is true.

Fifth question:

When it moves in south direction, there is no change in magnetic flux. Hence, induced current is zero. So, its false.

Sixth:

Using same previous argument, we can show that the induced current is zero. So, its true.

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