K.C.S.E Physics Q & A - MODEL 2009PP2QN18

K.C.S.E Physics Q & A - MODEL 2009PP2QN18

​(a) It is observed that when ultra- violet radiation is directed onto a clean zinc plate connected to the cap of a negatively charged leaf electroscope, the leaf falls
(i) Explain this observation 
(ii) State why this observation does not occur if the electroscope is positively Charged 
(iii) Explain why the leaf of the electroscope does not fall when infra- red radiation is directed onto the zinc plate

(b) State the effect on the electrons emitted by the photoelectric effect when:
(i) The intensity of incident radiation is increased
(ii) The frequency of the incident radiation is increased
(c) The maximum wavelength required to cause photoelectric emission on a metal surfaces is 8.0 x 10^-7m. The metal surface is irradiated with light of frequency 8.5 x 10¹⁴ Hz.
Determine:
(i) The threshold frequency
(ii) The work function of the metal in electron volts
(iii) The maximum kinetic energy of the electrons
Take: leV= 1.6 x 10^-19J.
Speed of light = 3.0 x 108 ms^-1
Plank's constant, h = 6.63 x 10^-34 Js

answers