A metal surface is illuminated with photons of energies $E_1=4 \mathrm{eV}$ and $E_2=2.5 \mathrm{eV}$ respectively. The ratio of maximum speeds of the photoelectrons in two cases is 2 . Work function of metal surface will be
A germanium crystal is doped with arsenic atoms and indium atoms simultaneously. Number of arsenic atoms used $=5 \times 10^{22}$ per $\mathrm{m}^3$ and number of indium atoms used $=5 \times 10^{20}$ per $\mathrm{m}^3$, then resulting crystal is a/an
In a car lift, compressed air exerts a force $F_1$ on a small piston having a radius of 5.0 cm . This pressure is transmitted to a second piston of radius 10.0 cm . If the mass of the car to be lifted is 1350 kg . The force on a small piston is
The magnitude of resistance $X$ in the circuit shown below in the figure, when no current flows through the $5 \Omega$ resistor, is