$A$ gamma ray photon creates an electron-positron pair. If the rest mass energy of an electron is $0.5\, MeV$ and the total kinetic energy of the electron-positron pair is $0.78\, MeV$,then the energy of the gamma ray photon must be $......\, MeV$.

When a current of $2\, A$ flows in a battery from negative to positive terminal,the potential difference across it is $12\, V$. If a current of $3\, A$ flows in the opposite direction,the potential difference across the terminals of the battery is $15\, V$. The $emf$ of the battery is ................ $V$.

$A$ student records $\Delta Q, \Delta U$ and $\Delta W$ for a thermodynamic cycle $A \to B \to C \to A$. Certain entries are missing. Find the correct entry from the following options.

Process	$AB$	$BC$	$CA$
$\Delta W$	$40 \ J$	$ $	$30 \ J$
$\Delta U$	$ $	$50 \ J$	$ $
$\Delta Q$	$150 \ J$	$10 \ J$	$ $

$A$ straight line is equally inclined to all the three coordinate axes. Then,the angle made by the line with the $y$-axis is

Charges of $2 \mu C$ and $-3 \mu C$ are placed at two points $A$ and $B$ separated by $1 \ m$. The distance of the point from $A$,where the net potential is zero,is (in $m$)

Equilibrium constant for the reaction $H_2O_{(g)} + CO_{(g)} \rightleftharpoons H_{2(g)} + CO_{2(g)}$ is $81$. If the velocity constant of the forward reaction is $162 \ L \ mol^{-1} \ s^{-1}$,what is the velocity constant (in $L \ mol^{-1} \ s^{-1}$) for the backward reaction?