A Microwave source emits a pulse of radiation at 1 GHz with a total energy of 1 J. The number of photons in the pulse is

Q. Lifetimes of the molecules in the excited state are often measured by using pulsed radiation source of duration nearly in the nano second range. If the radiation source has the duration of 2 ns and the number of photons emitted during the pulse source is $2.5\times {10}^{15}$, calculate the energy of the source.

Q. An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency $10GHz$. What is the frequency of the microwave measured by the observer?
(speed of light $=3\times {10}^{8}m{s}^{-1}$)

Q. An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency $10\text{GHz}$. What is the frequency in GHz of the microwave measured by the observer?
(speed of light $=3\times {10}^8{\text{ms}}^{-1}$). Answer the nearest integer.

Q. A laser used to weld detached retains emits light with a wavelength $652$ nm in pulses that are of $20ms$ duration. The average power during each pulse is $0.6W$. The energy in each pulse and in a single photon are :

Q. A ruby laser produces radiations of wavelengths, 662.6 nm in pulse duration are 10${}^{-6}$s. If the laser produces 0.39 J of energy per pulse, how many photons are produced in each pulse?