1. (a) A man pushes a heavy rock resting on the ground, but it does notmove. A student says that this is because the pushing force is

balanced by the reaction of this force. Comment, with the aid of a

diagram, on whether the student's argument is correct. (2 marks)

(b) Using a spring balance, a small object is found to weigh heavier at

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 again at

the two places using a beam balance ? Explain briefly.

(5 marks)

(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. (3 marks)

(d) (i) The equation of state and kinetic theory equation of an

1Nmc2

ideal gas can be written as pV= nRT and pV =

State the meaning of the 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.)

(6 marks

2. (a) Plane monochromatic light waves of wavelength h are incidentnormally 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.

(5 marks)

(b) Describean experiment for observing the absorption spectrum of

iodine using a diffraction grating. Describe the spectrum observed

and account for it in terms of the quantum nature of light and

atomic structure. (8 marks)

(c) Briefly explain the principles involved in identifying the elements

present in the atmosphere of the sun through studying the sun's

spectrum. (3 marks)

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. (3 marks)

(b) (i) An isolated spherical conductor is positively charged.

Draw carefUlly on the same diagram

(I) the electrostatic lines of 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.

(6 marks)

(c) With the aid of a diagram, describe and explain an experiment toinvestigate the potential around a charged sphere. Briefly describe

the experimental results. (7 marks)

4. (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. (5 marks)

(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 generator to provide a d.c. to a light

bulb using tjle method in (i) Ismoothing 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.

(11 marks)

5. (a) (i) With the aid of a labelled diagram, explain the workingprinciples of a diffusion cloud chamber. State, with brief

explanations, TWO properties of the radiations that

could be investigated by the cloud chamber.

(ii) The tracks of an a-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 a-particle and a helium

atom. Show, with mathematical derivation, how the mass

of an a-particle can be deduced from these tracks. (The

speed of the helium atom before collision is assumed to be

negligible.)

(10 marks)

(b) Explain, through analogous comparison with throwing dice, what

is meant by radioactive decay being a 'random process'. Hence

deduce from first principles the esponential law of decay of a

radioactive source. (No need to describe the dice esperiment.)

(Given : I~ = Inx+C ) (6 marks)