(a)(i) What is meant by the term artificial radioactivity?
(ii) Complete the table below
Emission
Nature
Charge
Ionizing
High speed electron
Moderately ionizing
Neutral
Negligible ionizing ability
Alpha particles
Positive
(b) In an x-ray tube, an electron is accelerated from rest towards a metal target by a 30 kV source. Calculate the kinetic energy of the electron. [e=1.6 x 10\(^{-19}\)C]
(c) The table below shows the frequencies of radiations incident on a certain metal and the corresponding kinetic energies of the photoelectrons.
Frequency x 10\(^{14}\)(Hz)
6.8
8.0
9.2
10.0
11.0
Kinetic energy x 10\(^{-19}\)(j)
0.8
1.6
2.4
2.9
3.8
(i) Plot a graph of kinetic energy, K.E, on the vertical axis and frequency, f, on the horizontal axis starting both axes from the origin (0,0).
(ii) From the graph, determine the:
i. Planck's constant;
ii. Threshold frequency of radiations;
iii. Work function of the metal.
Verified Correct Answer: .
Physical Principles & Numerical Solution
(a)() Meaning of artificial radioactivity;
The process by which a stable nucleus is bombarded with a neutron to make it unstable and so disintegrates/decays with the emission of particles/radiation and. energy.
Emission
Nature
Charge
Ionizing
Beta (\(\beta\))
High speed electron
Negative
Moderately ionizing
Gamma (\(\gamma\))
Electro-magnetic radiation
Neutral
Negligible ionizing ability
Alpha particles
Helium nucleus
Positive
Highly ionizing
(b) Calculation of kinetic energy
K.E = eV
= 1.6 x 10\(^{-19}\) x 30 x 10\(^{3}\)
= 4.8 \times 10\(^{-15}\)J
(c)(i) graph of K.E versus f
i. Both axes correctly distinguished
ii. Reasonable scale on both axes
(ii) (I) Planck's constant. h = slope of the graph Slope
i. \(\bigtriangleup\)K.E and \(\bigtriangleup\)f correctly determined
ii. \(\frac{\bigtriangleup K.E}{\bigtriangleup f}\) corectly determined and recorded within range.
(II) Threshold frequency, \(f_0\) .
The intercept on the horizontal or frequency axis.
(III) Threshold frequency, \(W_o\)
Negative intercept on K.E axis.
Source: Myschool Past Questions Archive (Record #63727)