The ratio of energies of photons with wavelengths $\lambda_1 = 150 \ nm$ and $\lambda_2 = 300 \ nm$ is:

Find the number of photons emitted per second by a $10 \ kW$ radio transmitter operating at a wavelength of $500 \ m$.

Monochromatic light of wavelength $3000 \, \mathring{A}$ is incident on a surface of area $4 \, cm^2$. If the intensity of light is $150 \, mW/m^2$, then the rate at which photons strike the target is:

Monochromatic light of frequency $6 \times 10^{14} \,Hz$ is produced by a laser. The power emitted is $2 \times 10^{-3} \,W$. How many photons per second on an average are emitted by the source? (Given $h = 6.63 \times 10^{-34} \,Js$)

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 the emitted radiation falls in the microwave region,the device is termed as