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01 AL Physics/Essay/P.1
HONG KONG ADVANCED LEVEL EXAMINATION
AL PHYSICS
2001 Essay Type Question
1. (a) (i) What is meant by inertia? Briefly explain its relation to force.
(ii) Use an example to illustrate that an object may not necessarily be at rest
when the net force acting on it is zero.
(3 marks)
(b) (i) Give an example in which a body is accelerating but its speed remains
unchanged. Briefly explain the motion by using the concepts of force and
the change of momentum.
(ii) Briefly outline an experiment to show the following relation:
force  mass  acceleration
Under what condition(s) would the relation become an equation? (8 marks)
(c) By considering a head-on collision between two moving spheres of different
masses, show clearly that the principle of conservation of momentum follows
from Newton’s laws of motion.
(5 marks)
2. (a) Distinguish between mechanical and electromagnetic waves in terms of their
nature and propagation. State the factors governing the speed of mechanical
waves in a solid.
(3 marks)
(b) (i) Describe an experiment, involving a double-slit arrangement, to
demonstrate the wave nature of light and to estimate its wavelength.
(ii) What further evidence would suggest that a light wave is (I)
electromagnetic and (II) transverse?
(7 marks)
(c) What is the principle of superposition? Use this principle to explain (i) the
formation of beats and (ii) the formation of stationary waves.
(6 marks)
3. (a) Define electric field intensity and electric potential at a point in an electric
field. Derive a relationship between these two quantities.
(4 marks)
(b) (i) What do you understand by the capacitance of an isolated conductor?
Suggest TWO practical applications of capacitors.
01 AL Physics/Essay/P.2
(ii) With the aid of a diagram, explain how the electric potential and the
capacitance of a positive charged, isolated conductor would be affected by
a neutral isolated conductor nearby.
(6 marks)
(c) Describe a method of measuring the capacitance of a parallel-plate air capacitor
using a reed switch. Discuss the factors limiting the accuracy of the method.
(There is no need to describe the mechanism of the reed switch.)
(6 marks)
4. (a) (i) Explain how the SI unit of magnetic field strength, the tesla, is defined.
(ii) Explain why two infinitely long straight wires carrying currents in the
same direction exert forces on each other.
(3 marks)
(b) Describe how you would produce a uniform magnetic field using a currentcarrying conductor. Briefly describe an experiment using a Hall probe to show
that the field is uniform.
(6 marks)
(c) A metal rod PQ of length l is moved with constant velocity v across a uniform
magnetic field of flux density B as shown. A potential difference of magnitude
Blv is developed across PQ.
P
uniform magnetic
field (into paper)
v
l
Q
(i) By considering the force(s) acting on an electron in the rod, explain how
the potential difference is developed and why it remains constant.
(ii) Show that the result is consistent with the law of electromagnetic
induction.
(iii) What would the situation be if the rod is moved with acceleration?
Explain briefly.
(7 marks)
01 AL Physics/Essay/P.3
5. (a) Give TWO pieces of experimental evidence which support the nuclear model
of an atom with energy levels. Briefly explain the implications associated with
these pieces of experimental evidence.
(4 marks)
(b) The energy levels of a hydrogen atom, in eV, are given by
En = -13.6/n2
where n = 1, 2, 3, …
(i) With the aid of an energy level diagram, explain the terms ground state
and ionization potential as applied to a hydrogen atom.
(ii) Describe TWO ways to bring about excitation of a hydrogen atom. How
does the concept of energy levels explain the emission line spectrum of
hydrogen?
(7 marks)
(c) Under certain circumstances, electrons can be emitted from substances by
photoelectric effect, thermionic emission or radioactivity. For each process,
briefly describe the condition(s) for electron emission and compare the
maximum kinetic energy of the emitted electrons.
(5 marks)
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