The figures below show two different situtions where a current may be induced in

Question

The figures below show two different situtions where a current may be induced in a loop according to Faraday's Law, with the direction given by Len's Law. The magnetic field strength in Figure 2 is represented by the density of crosses. Select true or false for the current in the loop. The cardinal direction are as defined in the compase rose.

Fig 1: Magnet moving east, induced current "a"

Fig 2: Loop moving East, induced current "a"

Fig 2: loop moving noth, induced current "a"

Fig 1: magnet moving west, induced current "a"

Fig 2: loop moving west, no induced current

Fig 1: loop moving west, induced current "a"

Explanation / Answer

When an emf is generated by a change in magnetic flux according to Faraday's Law, the polarity of the induced emf is such that it produces a current whose magnetic field opposes the change which produces it. The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant.

If the B field is increasing, the induced field acts in opposition to it. If it is decreasing, the induced field acts in the direction of the applied field to try to keep it constant.

With above theory, you can answer these questions.

Magnetic field lines of a bar magnet travel from north pole to the south pole outside the magnet. Thus, as the bar magnet is moved westwards, the net flux of magnetic field through the loop increases and this flux is towards right (i.e. south pole of magnet). To oppose that, a current is induced along 'b' so that the flux of magnetic field due to induced current is towards left (opposite right).

When magnet moves east, opposite of above happens and induced current is along 'a'.

When loop moves north, magnetic flux into the plane of paper increases (as density of dots increases), hence the current is anti-clockwise (outward magnetic field) to oppose that flux. Induced current, therefore is along 'a'.

For loop moving east or west, there is no change in flux hence no induced current.

Thus, answers are:

True, False, True, False, True and False respectively.

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