The ground state energy of hydrogen atom is -13.6 eV . The potential energy of the electron in this state is

If the energy released per fission of a ${ }_{92}^{235} \mathrm{U}$ nucleus is 200 MeV . The energy released in the fission of 0.1 kg d ${ }_{92}^{235} \mathrm{U}$ in kilowatt - hour is

The semiconductor used for fabrication of visible LEDS must at least have a band gap of

In a common emitter amplifier, AC current gains 40 and input resistance is $2 \mathrm{k} \Omega$. The load resistance is given as $10 \mathrm{k} \Omega$. Then, the voltage gain is