Question 12
(a) (i) State the difference between the production of X-rays and photoelectric effect.
(ii) Differentiate between line spectrum and continuous spectrum
(b) A particle of mass 2.0 x 10-4 kg moves with a speed of 300 ms-1. Calculate the associated wavelength of the particle. [h = 6.6 x 10-34 Js]
(c)(i) State the law of radioactive decay.
(ii) The activity of a sample is 326 Bq. If the original number of atoms in the sample is 1200, determine the:
(I) decay constant;
(II) half-life.
(d) The mass defect in a nuclear reaction is 0.5213 u. Calculate the binding energy
[1 u = 931 MeV; 1 eV = 1.6 x 10-19 J]
Observation
Part (a) Candidates performance was below average.
Part (b) Performance was below average.
Part (c) Candidates performance was average.
Part (d) Performance was below average.
The expected answers are:
(a) (i) Difference between the production of X-rays and photoelectric effect
In the production of x-ray, electrons collide with metals to produce x-rays (photons) while in photoelectric effect, metals absorbs light (photon) to eject electrons.
(ii) Differentiating between line spectrum and continuous spectrum
Line spectrum contains a well-defined light of a particular frequency/wavelength/colour while continuous spectrum contains light of all colour/wavelength/frequency.
(c) (i) The law of radioactive decay
The time rate of decay of a radioactive nuclide/nucleus is directly proportional to the number of nuclides/nuclei present.
OR
The activity of a radioactive nuclide/nucleus is directly proportional to the number of nuclides/nuclei present.
OR
The probability per unit time that a nucleus will disintegrate/decay is a constant, independent of time.
