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PhysicsSingle correct+3 / -1Question 46 of 60

IIT-JEE 2009 · Paper 1, Physics question 46

The figure shows certain wire segments joined together to form a coplanar loop. The loop is placed in a perpendicular magnetic field in the direction going into the plane of the figure. The magnitude of the field increases with time. I1I_1 and I2I_2 are the currents in the segments ab and cd. Then,

A single wire forming two nested squares in a uniform field into the page (crosses): the outer square's top side runs from c (left) to d (right) and the inner square's top side from a (left) to b (right); at the bottom-right corner the wire crosses over from one square to the other, so the two squares are traversed in opposite senses.
Choose one option
Answer and worked solution

Official answer: D

One loop. The wire forms a single circuit, so the same current flows in ab and cd: I1=I2I_1=I_2, and (A), (B) are out.

Direction. The loop goes round the outer square and the inner square in opposite senses (it crosses over at the corner). The flux into the page increases, so the induced emf drives an anticlockwise current in each square on its own; the outer square encloses more flux, so its emf wins. The current is anticlockwise round the outer square (along its top from d to c) and therefore clockwise round the inner square (along its top from a to b).

(D)

Topics:Faraday's and Lenz's laws
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