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
