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 Physics Paper 2, Nov/Dec. 2009
 Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
Weakness/Remedies
Strength

Question 15
Part II:      Candidates were required to answer any five questions from this part.
1. (a) (i)   A radioactive substance emits α, β and γ radiations.  Arrange them in order of decreasing;
(A)   penetrating power;
(B)   ionizing power.

(ii)   With the aid of a labelled diagram, explain how the radiations in (i) above are affected
by a magnetic field placed perpendicularly to the source.

(b)         State one factor each that is responsible for the:
(i)         occurrence of photoemission;
(ii)        number of electrons emitted during photoemission;
(iii)       energy of photoelectrons.

(c)        A photon has a frequency of 5.02 x 1014 Hz.
Calculate the energy of the photon in:
(i)         joules;
(ii)        electron volts.
[h = 6.6 x 10-34 Js;  1eV = 1.6 x 10-19 J]

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Observation

Part (a) was well attempted.  However, many of the candidates drew the expected diagram carelessly and so lost valuable marks.  One such example is given below:

Part (b) was fairly well attempted.
Part (c) was well attempted by the responding candidates.

(a)      (i)          (A)       gamma rays → beta rays →  alpha particles.

(B)       alpha particles → beta rays → gamma rays.

Accept:    γ → β →  α   and
α → β  → γ
(ii)

β ray is strongly deflected  (because it is negatively charged.

1. α particle is deflected but not as strong as the  β  - beta (because it is massive)
2. γ rays is not affected (because it has neither  charge nor mass).

(i)  -     The energy/frequency of incident radiation must be greater than thework function/threshold frequency of the metal
(ii)  -   the intensity of the radiation