K.C.S.E Physics Q & A - MODEL 2018PP2QN16

K.C.S.E Physics Q & A - MODEL 2018PP2QN16

​(a) State the meaning of the following terms:
(i) Photoelectric effect 
(ii) Threshold frequency 
(b) Figure 5 shows some light incident on the cathode of a photocell. The photocell is connected in series with a battery, a variable resistor and a microammete

​(î) Explain how the microammeter reading is affected when the intensity of the incident light is increased. 
(ii) State the reason why the tube is evacuated 
(c) Figure 6 shows a graph of maximum kinetic energy (KE max) of photoelectrons against the frequency of the incident radiation.

From the graph, determine:
(i) Plank’s constant h,
(ii)the threshold wavelength given that the speed of light C is 3.0 x 10⁸ms^-1

answers

​(a)(i) The emission of electrons from a metal surface when light/electromagnetic radiations shine on it. 
(ii) The minimum frequency of radiation required to eject electrons from a metal surface. 
(b)(i) Increased intensity increases the number of electrons emitted hence a higher current reading on the microammeter. 
(ii) To minimize collisions between electrons and air molecules which would cause loss of energy.