$A$ $160 \,W$ light source is radiating light of wavelength $6200 \,\mathring A$ uniformly in all directions. The photon flux at a distance of $1.8 \,m$ is of the order of .......... $m^{-2} s^{-1}$ (Planck's constant $= 6.63 \times 10^{-34} \,J \cdot s$)

$A$ proton moving with a momentum $p_{1}$ has a kinetic energy $1/8$th of its rest mass-energy. Another light photon having energy equal to the kinetic energy of the proton possesses a momentum $p_{2}$. Then,the ratio $\frac{p_{1}-p_{2}}{p_{1}}$ is equal to

Two sources of light emit $X$-rays of wavelength $1 \ nm$ and visible light of wavelength $500 \ nm$,respectively. Both sources emit light of the same power $200 \ W$. The ratio of the number of photons emitted per second by the $X$-ray source to the number of photons emitted per second by the visible light source is:

The principle of $LASER$ action involves:

$A$ photon of wavelength $4400 \ \mathring A$ passes through a vacuum. Its effective mass and momentum are,respectively,............

If $h$ is Planck's constant in $SI$ system,the momentum of a photon of wavelength $0.01 \, \mathring{A}$ is: