K.C.S.E Physics Q & A - MODEL 2017PP2QN16

K.C.S.E Physics Q & A - MODEL 2017PP2QN16

​(a) Figure 7 shows a set up that may be used to observe photoelectric effect. A radiation is incident on the cathode. it is observed that the microammeter registers a current.

(i) Explain how the current is produced.
(ii) State with a reason what must be done for a higher current to be registered.
(iii) It was observed that for a certain incident radiation, no current was registered.
Explain this observation.
(b)A monochromatic light of wavelength 4.50 X 10^-7 m is incident on a metal surface of threshold frequency 5.5 X 10¹⁴ Hz. (Speed of light c is 3.0 X 10⁸ms and planks constant h is 6.63 X 10^-34Js).
Determine
(i) the work function of the metal surface,
(ii) average kinetic energy of the emittal photoelectrons.

answers

 a)i. Radiations cause photo electrons to be ejected from the metal surface (cathode), the electrons are attracted by the anode hence  current flows.
ii)Source is made moved closer! increase anode voltage/accelerating voltage.
iii. The frequency of the incident radiation is below the thrsio1d frequency of the surface hence no emission can take place.