$1 \ J$ is equal to how many electron volt?

$A$ source $S_1$ is producing $10^{15}$ photons per second of wavelength $5000 \; \mathring{A}$. Another source $S_2$ is producing $1.02 \times 10^{15}$ photons per second of wavelength $5100 \; \mathring{A}$. Then,$(\text{power of } S_2) / (\text{power of } S_1)$ is equal to

$A$ photon creates an electron-positron pair with equal kinetic energy. If the kinetic energy of each particle is $0.29 \ MeV$,the energy of the photon must be .......... $MeV$.

If a photon has velocity $c$ and frequency $\nu$,then which of the following represents its wavelength?

The minimum intensity of light to be detected by the human eye is $10^{-10} \ W/m^2$. The number of photons of wavelength $5.6 \times 10^{-7} \ m$ entering the eye,with a pupil area of $10^{-6} \ m^2$,per second for vision will be nearly:

$A$ lamp of power $942 \ W$ radiates energy uniformly in all directions. The wavelength of radiation is $660 \ nm$. The photon flux on a small screen $5.0 \ m$ from the lamp in units of $\frac{\text{photon}}{m^2 \cdot s}$ is (Take Planck's constant $h = 6.6 \times 10^{-34} \ J \cdot s$ and speed of light $c = 3 \times 10^8 \ m/s$)