$A$ radio transmitter transmits at a frequency of $880 \ kHz$ and consumes $10 \ kW$ of power. The number of photons emitted per second from the transmitter is:

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

$A$ 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 minimum intensity of light that can be perceived by the human eye is $10^{-10} \ W/m^2$. If the area of the pupil is $10^{-6} \ m^2$ and the wavelength of light is $560 \ nm$,approximately how many photons per second enter the eye? (Use $h = 6.6 \times 10^{-34} \ J \cdot s$ and $c = 3 \times 10^8 \ m/s$).

Light from a source travels out with a velocity $c$. If the source moves away from the observer with a velocity $v$,then the relative velocity of light with respect to the observer is

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