Physics Paper 2 WASSCE (PC), 2019

 

Question 12

(a) What are thermoelectrons?

 

(b) State one function each of the following components of an x-ray tube in use: (i) low voltage battery;
(ii) target metal.

 

(c) Distinguish between α-particle and β-particle in terms of their: (i) nature;
(ii) charge.

 

(d) (i) State the radioactive decay law.
(ii) State two dangers associated with exposure to radioactive radiations

 

Observation

Part (a): Performance was below average.
Part (b): Performance was below average.
Part (c): Performance was poor.
Part (d): Performance was poor. Very few candidates made attempt.
The expected answer is :

12(a)Thermoelectrons
Negative charges that are released from the surface of heated metal

 

(bi) Function of low voltage battery in an x-ray tube
To heat up the filament to release electrons

 

(ii) Function of target metal in x-ray tube
- To stop fast moving electrons
- Production of x-rays

 

(ci) Distinction between α particle and β particle in terms of their nature
α is helium nucleus while β is fast moving electron

 

(ii) Distinction between α particle and β particle in terms of their charge
αis positively charged
while
β is negatively charged

 

(d) The radioactive decay law
States that the amount of nuclei decaying/disintegrating per unit time is proportional to the number of nuclei present at the time.
OR
The probability per unit time that a nucleus will decay is a constant independent of time.

 

(i) Dangers associated with exposure to radioactive radiations
- Damage/irritation of the eye
- Skin-burn/tanning
- Cell mutation
- Cancer/leukaemia

 

(ei) Determination of the values of m and n

 

(eii) Calculation of the neutron-proton ratio of

(iii) X is unstable