Question

Calculate the number of photons emitted per second by a transmitter of 10 kW power, emitting radio waves of wavelength 500 m. 

Solution

Correct option is

The electromagnetic energy radiated by the transmitter is given by

        

            

            

Let n be the number of photons emitted per second by the transmitter. Since the energy of each photons is hv, we have 

        

            

     

            

            .

Thus, the number of photons emitted per second in a radio beam is enormously large. Correspondingly, the energy of a ratio-photon is exceedingly small . Hence, ratio engineers do not worry about photons and treat the energy of a ratio wave as continuous. 

SIMILAR QUESTIONS

Q1

The maximum frequency of the X-rays produced in an X-ray tube

Q2

Which one of the following parameters of the emitted X-rays increases when the potential difference between the electrodes of an X-ray tube is increased?  

Q3

Calculate the energy of a photon, in electron-volt (eV) and in watt-hour (W h), of wavelength 6600 Å. 

Q4

An X-rays tube produces a continuous spectrum of radiation with its short wavelength end at 0.45 Å. What is the maximum energy of a photon in the radiation? What is the order of accelerating voltage (for electrons) required in such a tube? 

     

Q5

 

In an accelerator experiment on high-energy collisions of the electrons with positrons, a certain event is interpreted as the annihilation of an electron-positron pair of total energy 10.2 BeV into two -rays of equal energy. Find the wavelength associated with each -ray. 

Q6

Energy from Sun is received on earth at the rate of . If average wavelength of solar light is taken as 550 nm, then how many photons are received on earth per meter2 per second? 

Q7

Monochromatic light of frequency  is produced by a laser. The power emitted is . What is the energy of a photon in the light beam?

Q8

A beam of green light  gives energy at the rate of 1 Js–1 to a surface where it is fully absorbed. How many photons reach the surface per second? If every 100 photons emit one electron, how much current will flow from the surface? 

Q9

 

Calculate the number of photons emitted per second by a transmitter of 10 kW power, emitting radio waves of wavelength 500 m. 

Q10

The minimum light intensity that can be perceived by human eye is about 10–10 Wm–2. Find the number of visible-light photons that must enter the pupil of our eye per second for vision. Take the area of the pupil to be about 0.4 cm2 and the average wavelength of visible light to be 5000 Å.