question_answer

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

A)  the photo- current will increase

B)  the kinetic energy of the electrons will increase

C)  the slopping potential will decrease

D)  the threshold wavelength will increase  

Correct Answer: B

Solution :

In electric field photoelectrons will experience force and accelerate opposite to the field so its KE increases (ie, stopping potential will increase), no change in photoelectric current, and threshold wavelength.