Question 12
(a) State two sources of background radiation.
(b) Why is the count rate of background radiation not constant at a particular place?
(c) Name two materials that cannot be dated using carbon dating.
(d) Name the types of nuclear radiation, that can be used to detect leakage in an underground pipe.
(e) Two metal surfaces X and Y of work functions 2.90 eV and 4.82 eV respectively are each illuminated by light of wavelength 330 nm.
(i) which of the surfaces will emit photoelectrons? Justify your answer by calculation.
(ii) Calculate the kinetic energy of the photoelectrons.
[h = 6.6 x 10-34 Js; c = 3.0 x 108 ms-1; 1 eV = 1.6 x 10-19 J]
Observation
Part (a): Performance was below average. Few candidates who attempted the question were able to score full mark.
Part (b): Performance was below average.
Part (c): Performance was fair.
Part (d): Performance was fair.
Part (e): Performance was fair. Many candidates supplied the response but was unable to support the claim with calculation.
The expected answers are:
12.(a) Sources of Background Radiation
e.g
- air;
- earth/ground/rock;
- sun;
- sea;
- galaxy;
- star;
- nuclear weapon testing/accident;
(b) Radiation background count rate is not constant at a place because radioactive decay is a random and continuous process
(c) Carbon Dating Not Applicable
e.g
- brick;
- rock;
- metal.
(d) Detection of Leakage
gamma
