The energy of a photon with a wavelength of $6.20 \times 10^{-5} \ cm$ is ....... $eV$.

Let $n_r$ and $n_b$ be respectively the number of photons emitted by a red bulb and a blue bulb of equal power in a given time.

The energy of a photon with a wavelength of $\lambda = 4000 \ \mathring{A}$ is equal to ........ Joules.

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:

$A$ parallel beam of light of wavelength $900 \, nm$ and intensity $100 \, W/m^2$ is incident on a surface perpendicular to the beam. The number of photons crossing $1 \, cm^2$ area perpendicular to the beam in one second is:

The eye can detect $5 \times 10^4$ photons per square metre per second of green light $(\lambda = 5000 \ \mathring{A})$ while the ear can detect $10^{-13} \ W/m^2$. The factor by which the eye is more sensitive as a power detector than the ear is close to: