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? 


Correct option is

As in previous example, the energy of a light-photon of wavelength  is  


1 joule of energy reaches on the surface per second.    

 number of electrons reaching is  


100 photons emit one electron. Hence, the number of electrons emitted is 


1 electron has a change of . Hence the charge received from the surface is  


Rate of the flow of charge is the current. Hence electric current is 




X-rays which can penetrate through longer distance in substances are called.


The target in an X-rays tube should be a:


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


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?  


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


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? 




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. 


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? 


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



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