If photoelectrons are to be emitted from a potassium surface with a speedof , what frequency of radiation must be used? The threshold frequency for potassium is 


Correct option is

If v be the frequency of incident radiation and v0 the threshold frequency, then 


Where  is the maximum speed of emitted photoelectrons. From this, we have 







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. 


A 5-W point-source emits monochromatic light of wavelength 5000 Å. How many photons per second strike a unit area placed 5 m away from the source and illuminated by it? What should be the work function of the metal from whose surface this light can liberate photoelectrons? 



The wavelength of a photon is 1.4 Å. It becomes 2.0 Å after a collision with an electron. Calculate the energy of the scattered electron. 



Find the moment and equivalent mass of a photon of radiation of wavelength 3300 Å. 


An isolated hydrogen atom emits a photon of energy 10.2 eV. Calculate momentum of the photon. 


Light of wavelength 3500 Å is incident on two metals A and B. Which metal will emit photoelectrons, if their work functions are 4.2 eV and 1.9 eV respectively? 


A light beam of wavelength 6000 Å and intensity  falls normally on a photon-cathode of surface area 1 cm2 and work function 2 eV. Assuming that there is no loss of light by reflection etc., calculate the number of photoelectrons emitted per second. 


When a beam of 10.6-eV photons of intensity 2.0 Wm–2 falls on a platinum surface of area  and work function 5.6 eV, 0.53% of the incident photons eject photoelectrons. Find the number of photoelectrons emitted per second and their minimum and maximum energies (in eV). Take . 


The work function for cesium is 1.8 eV. Light of 5000 Å is incident on it. Calculate maximum velocity of the emitted electrons.


A sheet of silver is illuminated by monochromatic ultraviolet radiation of wavelength 1810 Å. What is the maximum energy of the emitted electrons? The threshold wavelength for silver is 2640 Å.