$A$ parallel plate capacitor of capacity $C_0$ is charged to a potential $V_0$. $(i)$ The energy stored in the capacitor when the battery is disconnected and the plate separation is doubled is $E_1$. (ii) The energy stored in the capacitor when the charging battery is kept connected and the separation between the capacitor plates is doubled is $E_2$. Then,the value of $E_1 / E_2$ is:

$A$ photon of energy $8\, eV$ is incident on a metal surface of threshold frequency $1.6 \times 10^{15}\, Hz$. The maximum kinetic energy of the emitted photoelectrons is ............. $eV$ $(h = 6.6 \times 10^{-34}\, Js)$.

The figure below shows two paths that may be taken by a gas to go from a state $A$ to a state $C$. In process $AB$,$400 \, J$ of heat is added to the system and in process $BC$,$100 \, J$ of heat is added to the system. The heat absorbed by the system in the process $AC$ will be ............. $J$.

The tyre of a bicycle has a volume of $2 \times 10^{-3} ~m^3$. Initially,the tube is filled to $75 \%$ of its volume with air at an atmospheric pressure of $10^5 ~Nm^{-2}$. When a rider is on the bicycle,the area of contact of the tyre with the road is $24 \times 10^{-4} ~m^2$. The mass of the rider with the bicycle is $120 ~kg$. If a pump delivers a volume of $500 ~cm^3$ of air in each stroke,then the number of strokes required to inflate the tyre is $\left(g=10 ~ms^{-2}\right)$.

Two waves $Y_1 = 0.25 \sin 316 t$ and $Y_2 = 0.25 \sin 310 t$ are propagating in the same direction. The number of beats produced per second is

$A$ bag contains $2n+1$ coins. It is known that $n$ of these coins have a head on both sides,whereas the remaining $n+1$ coins are fair. $A$ coin is picked up at random from the bag and tossed. If the probability that the toss results in a head is $\frac{31}{42}$,then $n$ is equal to