The collector plate in an experiment on photoelectric effect is kept vertically above the emitter plate . Light source is put on and a saturation photo current is recorded . An electric field is switched on which has a vertically downward direction . Then

Options

A. the photoelectric current will increase
B. the kinetic energy of the electrons will increase
C. the threshold wavelength will increase
D. the stopping potential will decrease

Answer

B

Explanation

Initially `C_p` is + ve and `E_p` is -ve
`therefore` The electrons are attached upwards and a saturation current is obtained. When the electric field acting vertically downwards is applied, it will produce downward force on the + ve charges and an upward force on the negatively charged photoelectrons. Hence the electrons are accelerated and hence their velocity and kinetic energy will increase.
Thus (b) is the correct option.
There is no change is photoelectric current as well as threshold wavelenght and we have to increase the stopping potential to retard the motion of energetic electrons. Thus, (a) (c) and (d) are wrong.