Question

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. 

Solution

Correct option is

1012

The energy of a photon of wavelength  is 

      

          

          

          = 2.06 eV. 

The work function of the surface is 2 eV. Thus, the energy of photon is greater than the work function of the surface. Hence, the incident light is able to emit photoelectrons. 

The number of photons falling on the surface of area 1 cm2 (= 10–4 m2) of the photocathode is

      

                              = 1012 s–1.

Assuming that each photon emits one photoelectron, the number of photoelectrons emitted per second is 1012.

SIMILAR QUESTIONS

Q1

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? 

Q2

 

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

Q3

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

Q4

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. 

Q5

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? 

  

Q6

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. 

  

Q7

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

Q8

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

Q9

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? 

Q10

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 .