A copper rod of mass m slides under gravity on two smooth parallel rails, with separation l and set at an angle of $$\theta $$ with the horizontal. At the bottom rails are joined by a resistance R. There is a uniform magnetic field B normal to the plane of the rails, as shown in the igure. The terminal speed of the copper rod is :

A plane polarized light is incident on a polariser with its pass axis aking angle $$\theta $$ with x-axis, as shown in the figure. At four different values of $$\theta ,\,\theta $$ = 8^o, 38^o, 188^o and 218^o, the observed intensities are same.
What is the angle between the direction of polarization and x-axis ?

Truth table for the following digital circuit will be :

A current of 1 A is flowing on the sides of an equilateral triangle of side 4.5 $$ \times $$ 10^-2 m. The magnetic field at the center of the triangle will be :