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97 AL Physics/Essay/P.1
HONG KONG ADVANCED LEVEL EXAMINATION
AL PHYSICS
1997 Essay Type Question
1.
(a) A man pushes a heavy rock resting on the ground, but it does not move. A
student says that this is because pushing force balanced by the reaction of
this force. Comment, with the aid of diagram on whether the student’s
argument is correct.
(b). Using s spring balance, a small object is found to weigh heavier the north
pole than at the equator.
(i) State and explain TWO reasons for this observation.
(ii) What would the result be if the object is weighed against the two
places using a beam balance? Explain briefly.
(c) Consider the cases in which (i) a man is inside a lift falling freely and (ii) he
is inside a space-craft moving in a circular orbit round the earth. Identify
THREE similarities between these physical environments.
(d) (i) The equation of state and kinetic theory equation of an ideal gas can be
written as pV  nRT and pV 
1
Nmc 2 . State the meaning of the
3
symbols excluding pressure p and volume V.
(ii) Two identical vessels containing hydrogen and oxygen respectively are
at the same temperature and pressure. What can you say about the
number of molecules, the average molecular kinetic energy and the
mean square speed of the molecules in the two vessels? Explain briefly
(Assume that the gases behave ideally.)
2.
(a) Plane monochromatic light waves of wavelength are incident normally
onto a plane transmission grating of slit separation d to produce an
interference pattern.
(i)
Using the principle of superposition describe briefly how the principal
maxima are formed and deduce the formula for the angular positions of
the principal maxima.
(ii) It is preferable to measure the wavelength of light by using a plane
transmission grating rather than using a double slit. Explain briefly.
(b) Describe an experiment for observing the absorption spectrum of iodine
using diffraction grating. Describe the spectrum observed and account for it
in terms of the quantum nature of light and atomic structure.
(c) Briefly explain the principles involve in identifying the elements present in
the atmosphere of the sun through studying the sun’s spectrum.
97 AL Physics/Essay/P.2
3.
(a) Explain the meaning of the potential difference between two points in an
electric field and hence state the meaning of the potential at a point in the
field.
(b) (i) An isolated spherical conductor is positively charged. Draw carefully
on the same diagram
(I) The electrostatic lines of the force,
(II) A series of equipotential surfaces with equal increment in electric
potential around the spherical conductor.
(ii) With reference to the diagram drawn in (i)
(I) Explain how the lines of force help in describing an electric field.
(II) Illustrate the relationship between electric field strength and
potential difference.
(c) With the aid of a diagram, describe and explain an experiment to investigate
the potential around a charged sphere. Briefly describe the experimental
4.
results.
(a) You are given two bar magnets, a long copper wire and a light beam
galvanometer. Describe how you would use the apparatus to investigate
qualitatively the factors affecting the e.m.f. induced in a coil by
electromagnetic induction.
(b) (i)
Consider a rectangular coil of N turns rotating uniformly in a uniform
magnetic field about an axis perpendicular to the field. Derive an
expression for the e.m.f. produced.
(ii) With the aid of a labelled diagram, describe the construction of a
5.
generator to provide a d.c to a light bulb using the method in (i)
[smoothing is not required]. Show that the current generated is always
flowing in one direction through the bulb.
(iii) Explain carefully why a greater driving torque is needed to maintain
the coil of the generator rotating at the original speed when an identical
light bulb is connected in parallel with the first one , Also explain how
this change agrees with the principle of conservation of energy.
(a) (i) With the aid of a labelled diagram, explain the working principles of a
diffusion cloud chamber, State , with brief explanations, TWO
properties of the radiations that could be investigated by the cloud
97 AL Physics/Essay/P.3
chamber.
(ii) The tracks of an source are observed in a diffusion cloud chamber in
which a trace amount of helium is introduced. Sketch the tracks
observed when there is an oblique collision between an -particle and
a helium atom. Show, with mathematical derivation, how the mass of
an particle can be deduced from these tracks. (The speed of the
helium atom before collision is assumed to be negligible.)
(b) Explain , through analogous comparison with throwing dice, what is meant
by radioactive decay being a ‘ random process’. Hence deduce from first
principles the exponential law of decay of radioactive source.( No need to
describe the disc experiment.)
(Given:

dx
 ln x  C )
x