Physics (Essay) Paper 2 WASSCE (SC), 2018

Question 12

 

(a)       Define binding energy in an atom.
(b)       List three evidences to support the claim that X-rays are electromagnetic waves.
(c)       List three peaceful uses of nuclear energy.
(d)       Light of wavelength 4.5 x 10-7m is incident on a metal resulting in the emission of photo electrons.  If the work function of the metal is 3.0 x 10-19 J, calculate the:
(i)        frequency of the incident light;
(ii)       energy of the incident light;
(iii)      energy of the photoelectrons.
[speed of light = 3.0 x 108 ms-1, h = 6.6 x 10-34 Js]

Observation

 

Part (a):    This question was popular among the candidates but unfortunately performance was fair. Many candidates stated the wrong definition.
Part (b):    Performance was fair although some candidates got only one right answer.
Part (c):    Performance was fair although some candidates wrongly cited nuclear bomb as an example of peaceful use of nuclear energy.
Part (d):    Many candidates scored full mark allotted to this question. Some however, still found it difficult to interpret the equation. Performance was below average.

The expected answer is:

12.(a) Binding Energy

Binding energy is the minimum work/energy required to separate the nucleons of an atom.                                                              
OR
The minimum work/energy required to remove an electron from the influence of the nucleus.                                
(b)   Required Evidences

  • Not affected by electric /magnetic fields
  • Can travel through a vacuum
  • Travels with the speed of light
  • Can be polarized
  • Causes fluorescence

(c)     Peaceful Uses

  • Generates electricity
  • Treatment of tumour
  • Power submarines/rockets

Food irradiation