Question 12
(a)(i) Define Isotopes.
(ii) Mention two uses of radioactive tracers in each of the following areas:
(α) medicine;
(ꞵ) industry;
(γ) agriculture.
(b) When light of frequency 5.4 x 1014 HZ is incident on a metal surface, the maximum energy of the emitted electrons is 1.2 x 10-19 J. calculate the minimum frequency of radiation for which electrons can be emitted. [h= 6.6 x 10-34 J s]
(c) State three features common to electromagnetic waves.
(d) (i) Mention four components of the nuclear reactor.f the components stated in 12(d)(i)
Observation
Part (ai): This question was popular among the candidates but unfortunately most of the candidates who attempted the questions could not define isotope correctly.
(ii)(α) Candidates mostly said that radioactive traces are used for treatment of disease and left out the aspect thst they are also used for diagnosis.
(ꞵ) Most candidates mostly wrote that they are used for detection of leakages in underground pipes.
(γ) Most candidates could not figure out what radioactive tracers are used for in Agriculture.
Part (b): Performance was fair. Candidates were expected to recall the equation E = h(f – fo), substitute and solve for fo but most of them used E = hf.
Part (c): Performance was good.
(d): Most candidates were unable to represent components of the nuclear reactor correctly. For example, instead of uranium fuel, candidates wrote fuel.
The expected answer is:
(a) (i) Definition of isotopes
Atoms of the same element that have the same number of
protons but different number of neutron.
OR
Same atomic number but different mass number
(ii) (a) Uses of Radioactive Tracers in Medicine
- monitoring the function of the thyroid gland / other organs
- detection of blood clots in the brain
- diagnosis and treatment of disease
- sterilization of medical equipment
(b) Uses of Tracers in industry
Detection of:
- leakages in underground pipes
- wear and tear of moving parts of machinery
- environmental pollution
(g) Uses of tracers in agriculture
- determination of plants absorbtion of mineral elements
- study of the mechanism of photosynthesis
- seed preservation
- sterilization of insects
- food preservation
(b) Calculation of minimum frequency of radiation
OR
= 
= 3.6 x 1014 Hz
(c) Features of electromagnetic waves
- Transverse waves
- Travel with the speed of light in vacuum
- Undergo refraction/reflection/diffraction/polarization/interference
- Travel through vacuu
(d) (i) Components of the nuclear reactor
- uranium fuel
- graphite moderator
- (boron) control rod
- coolant
- heat exchanger
- shield
(ii) Functions of the components of the nuclear reactor
uranium rods – serves as fuel
graphite moderator – controls neutron speed
(boron) control rod – control neutron population
coolant – reduces the excessive heat produced in the reaction
heat exchanger – converts the heat energy produced to other forms
shield – to protect the operator and surrounding against extraneous radiation