Marks
5. [a) Explain the terms total reflection and critical angle. (3)
Describe an experiment to determine the critical angle for an air-perspex
interface. If the critical angle is found to be 40 • 8° what is the value of the
refractive index air to perspex ? (6)
A beam of light strikes the mid-point of one side of a square slab of glass
of side 4 in. If the beam is at an angle of 30° to the side of the square, trace
the path of the beam through the glass, and state the point at which the
beam emerges and its angle of emergence. (6)
air g]ass — 1*5
[b) The focal length of a thin bi-convex lens is 20 cm. Find, from a carefully
drawn diagram, how far from the lens an object must be placed if the image
is to be erect and twice the height of the object. (5)
6. Account for the production of sound by a vibrating tuning fork. (3)
What do you understand by beats ? Explain carefully how they occur. (4)
You are given two tuning forks. One, which is marked C, gives a true middle C.
The other is very slightly different. How would you determine experimentally
how much this second fork was off tune and whether its note was higher or
lower than true C ? (6)
The wire of a horizontal monochord, supported on two bridges 1 metre apart,
weighs 2 x 10-3 gm per cm and is held taut by a weight of 2 kg hanging
vertically from a frictionless pulley. A third bridge is inserted and adjusted to
make one segment of the wire sound middle C (frequency 256) when plucked.
With what frequency does the other segment sound ? (7)
l- With the aid of a diagram describe the principle on which a moving-coil
galvanometer works. (4)
Give details of the experiment you would perform to calibrate a moving-coil
ammeter. " (8)
A sensitive moving-coil galvanometer has a resistance of 200 ohms and gives a
hill-scale deflection for a current of 0-005 amp. How can you adapt this
instrument to act as
(i) an ammeter of range 0-1 amp ? (4)
(ii) a voltmeter of range 0-1 Ov ? (4)
8- Define the coulomb and the volt. (4)
Sketch the circuit you would use to determine the resistance of a ware and
iscuss the two possible positions of the voltmeter. (6)
Draw the electric circuit wherein 8 cells each of internal resistance 0-5 ohm
and e.m.f. 2v are connected in series with a lamp labelled 12v 6w and two
rjS'sta®ce c°ils in parallel with each other. If one of the coils has a resistance
0 ohm what must be the resistance of the other to maintain the lamp at its
proper wattage ? (6)
If you wished to run two 12v 6w lamps from this battery what circuit would
You use? r ^
^ (turn over)
Page three