The primary of a transformer has 400 turns while the secondary has 2000 turns. If the power output from the secondary at 1000 V is 12 kW . The resistance of the primary is $0.2 \Omega$ and that of the secondary is $2 \Omega$. If the efficiency of the transformer is $80 \%$, then the power loss in the primary is
The maximum power rating of a $20 \Omega$ resistor is 2 kW . Then, it cannot be used with 300 V DC source because the
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