K.C.S.E Physics Q & A - MODEL 2019PP2QN19

K.C.S.E Physics Q & A - MODEL 2019PP2QN19

​(a) Define half life  as used in radioactivity. 
(b) Figure 13 shows a device used to detect radioactivity by forming tracks when air is ionised.

(i) State the name of the device shown.
(ii) State how air in the device gets ionised.
(iii) Describe how tracks are formed
(c) (i) State two factors that determine the speed of the photoelectrons emitted from a metal surface
(ii) The energy of a photon of light is 2.21 eV. (electronic charge is 1.6x10^-19C and planks constant h is 6.63x10^-34Js)
I. Express this energy in joules.
II. Determine the frequency of the light that produces the photon.

answers

​(a) Half life is the time taken for half the number of nuclides initially present in a sample to decay
(b). (ii) Expansion closed chamber
(ii) Due to collisions between the molecules from the radiations source and the air molecules
(iii) When the piston is pulled down air expands hence cools.
(c)(i) The work function of the metal
 Energy of incident radiation frequency/wavelength