The figure shows an isosceles triangle wire f | vedclass

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(B) Let the apex of the triangle be at the origin and moving along the $x$-axis. The length of the wire segment inside the magnetic field at time $t$

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(B) Let the apex of the triangle be at the origin and moving along the $x$-axis. The length of the wire segment inside the magnetic field at time $t$ is $l = 2(vt) 	an(\pi / 4) = 2vt$.The induced electromotive force (emf) is given by $\varepsilon = B l v = B(2vt)v = 2Bv^2t$.Since the resistance $R$ of the frame is proportional to its length,the resistance of the part inside the field is also proportional to $t$. Let $R = k t$ for some constant $k$.The induced current $i = \varepsilon / R = (2Bv^2t) / (kt) = (2Bv^2) / k$,which is a constant value.As the frame continues to enter,the length of the wire inside the field increases,but the resistance also increases proportionally,keeping the current constant until the entire frame is inside the field.Therefore,the current $i$ remains constant with time until the frame is fully inside the magnetic field,after which it becomes zero.Comparing this with the given options,the graph showing a constant current is represented by option $(b)$.

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