A black sphere has radius $R$ whose rate of radiation is E at temperature T . If radius is made half and temperature 4 T , the rate of radiation will be

If the ionisation energy for the hydrogen atom is 13.6 eV , then the energy required to excite it from the ground state to the next higher state is nearly

A closed pipe containing a liquid showed a pressure $P_1$ by gauge. When the valve was opened, pressure was reduced to $\mathrm{P}_2$. The speed of water flowing out of the pipe is ($\rho=$ density of water)

In a diffraction pattern due to single slit of width ' $a$ ', the first minimum is observed at an angle $30^{\circ}$ when light of wavelength $5000 \mathop A\limits^o$ is incident on the slit. The first secondary maximum is observed at an angle $\left[\sin 30=\frac{1}{2}\right]$