WAEC Physics 2020 Theory — Question 12

Model answer

(a)(i) Isotopes are atoms of the same element with the same number of protons (atomic number) but different number of neutrons (mass number). (ii) Uses of radioactive tracers in medicine: Monitoring the function of the thyroid gland and other organs; Detection of blood clots in the brain; Diagnosis and treatment of disease; Sterilization of medical equipment. Uses of tracers in industry: Leakages in underground pipes; Wear and tear of machinery; Environmental pollution. Uses of tracers in agriculture: Determination of plants absorption of mineral elements; Study of the mechanism of photosynthesis; Seed preservation; Sterilization of insects; Food preservation. (b) Given: f=5.4x10^14 Hz, Emax=1.2x10^-19 J, required fo=? Using Emax=hf-Wo, E=hf-hfo=h(f-fo), so fo=f-(1.2x10^-19)/(6.6x10^-34)=5.4x10^14-0.1818x10^15=5.4x10^14-1.188x10^14=3.6x10^14 Hz. (c) Features common to electromagnetic waves: They are transverse waves; travel with the speed of light in vacuum; undergo refraction, reflection, diffraction, polarization and interference; travel through vacuum. (d)(i) Components of the nucleus reaction/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 for the nuclear reaction; Graphite moderator - controls neutron population; Coolant - reduces the excessive heat produced in the nuclear reactor; Heat exchanger - converts the heat energy produced to other forms; Shield - to protect the operator and surrounding against extraneous radiations.