The time taken for the magnetic energy to reach 25% of its maximum value, when a solenoid of resistance R, inductance L is connected to a battery, is :

The magnetic field in a region is given by $$\overrightarrow B = {B_o}\left( {{x \over a}} \right)\widehat k$$. A square loop of side d is placed with its edges along the x and y axes. The loop is moved with a constant velocity $$\overrightarrow v $$ = v₀$$\widehat i$$. The emf induced in the loop is :

A conducting bar of length L is free to slide on two parallel conducting rails as shown in the figure


Two resistors R₁ and R₂ are connected across the ends of the rails. There is a uniform magnetic field $$\overrightarrow B $$ pointing into the page. An external agent pulls the bar to the left at a constant speed v.

The correct statement about the directions of induced currents I₁ and I₂ flowing through R₁ and R₂ respectively is :

An aeroplane, with its wings spread 10 m, is flying at a speed of 180 km/h in a horizontal direction. The total intensity of earth's field at that part is 2.5 $$\times$$ 10^$$-$$4 Wb/m² and the angle of dip is 60$$^\circ$$. The emf induced between the tips of the plane wings will be __________.