In a parallel plate air capacitor, a cathode beam comprising $n = 10^6$ electrons is emitted with a velocity $v_0 = 10^8\ m/s$ into the space between the plates. The potential difference between the plate is $\phi  = 400\ V$ ,the seperation between the plates is $d = 2\ cm$ and the area of each plate is $l^2 = 100\ cm^2$ . The deflection of the electron beam, is ……….. $mm$

If on the concentric hollow spheres of radii $r$ and $R( > r)$ the charge $Q$ is distributed such that their surface densities are same then the potential at their common centre is

An electric dipole is placed along the $x$ -axis at the origin $O.$ A point $P$ is at a  distance of $20\, cm$ from this origin such that $OP$ makes an angle $\frac{\pi}{3}$ with  the $x$ -axis. If the electric field at $P$ makes an angle $\theta$ with the $x$ -axis, the value of $\theta$ would be

The amount of heat liberated in the circuit after closing the switch $S$ .

Four charges are placed at the circumference of a dial clock as shown in figure. If the clock has only hour hand, then the resultant force on a charge $q_0$ placed at the centre, points in the direction which shows the time as