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 ........... $mm$

Two point charges placed at a distance $r$ in air experience a certain force. Then the distance at which they will experience the same force in a medium of dielectric constant $K$ is

Two charged spheres of radii $R_1$ and $R_2$ having equal surface charge density. The ratio of their potential is

Three capacitors $1, 2$ and $4\,\mu F$ are connected in series to a $10\, volts$ source. The charge on the plates of middle capacitor is

A charged particle $'q'$ is shot from a large distance with speed $v$ towards a fixed  charged particle $Q$. It apporaches $Q$ upto a closet distance $r$ and then returns. If $q$ were given a speed $'2v$', the closest distance of approach would be 

In the circuit shown, a potential difference of $30\, V$ is applied across $AB$ . The potential difference between the points $M$ and $N$ is....$V$