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Q. 7. A ray of light is incident at an angle of 30° on one face of an

equilateral prism. If the path of the light through the prism is parallel to the base, find the direction of the emergent ray, and the total deviation of the ray after passing through the

prism. Very easy and fairly well answered by those who tried it. Q. 8. An object at a distance of 10 inches from a lens, when viewed

through the lens, appears to be at a distance of 30 inches from the lens. Find the focal length of the lens, and give a diagram

showing the nature of the image. The answers to this question were either good or very bad.

HEAT. Q. 9. If the latent heat of fusion of ice is 80 calories per gramme, find

how much ice would be required to cool one kilogramme of

water from 20° C. to 10° C. Generally attempted and fairly done on the whole. Many omitted to allow for the heating of the melted ice from 0° to 10° C. Q. 10. A room contains 66 kilogrammes of air at 27° C. and 780 mm.

pressure. What will be the weight of air contained (a) if the

temperature falls to 2° C., (b) if the barometer falls to 715 mm.? Seldom tried. A few good answers, the rest worthless. Q. 11. Distinguish between evaporation and boiling. How is the boiling

point of a liquid defined, and how is it affected by pressure. The nature of ebullition was not well understood.

Q. 12. Describe some form of maximum, and some form of minimum

thermometer, and point out the defects (if any) of either

instrument. Seldom attempted, and little knowledge of details shown.

SOUND.

STAGE 2.

Results : 1st Class, 10; 2nd Class, 9; Failed, 10; Total, 29. A few of the papers were very bad, but the majority appeared to be of a fair order of merit. The number sent in was too small to permit of any general conclusions of value being drawn.

LIGHT.

STAGE 2.

Results : 1st Class, 19; 2nd Class, 34; Failed, 21 ; Total, 74.

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The answers to this paper were fair on the whole, with a normal proportion of good papers, and a similar proportion of failures. With regard to the several questions, the commonest mistakes made were those noted below, but many of the good papers were practically free from serious mistakes, and were clearly written and well expressed. Q. 1. What is meant by spherical aberration ?

Make a careful drawing of the manner in which parallel rays

are reflected by a hemi-spherical concave mirror. Many of the diagrams omitted the caustic curve,

Q. 2. Determine the limits of the angle of incidence of a ray of light on

one face of an equilateral prism so that the ray may be refracted

at the second face, assuming the critical angle to be 45°. The index of refraction was often taken as 3/2 instead of 12, and the angle of incidence wrongly deduced. Q. 3. Describe the method by which Fizeau observed the velocity of light,

indicating by a diagram the optical arrangements necessary. Little knowledge was shown of the optical arrangements. Q. 5. A rhomb of Iceland spar is laid on a page of print. How will the

appearance of the print differ from that which would be observed if the Iceland spar were replaced by a slab of glass? How does the appearance alter when the rhomb is rotated while still remaining in contact with the page

e? Many candidates thought that the brightness of the two images and their distance apart varied as the crystal was rotated. Q. 6. A short-sighted person cannot see objects clearly at a distance

greater than 6 inches. What spectacles would be required to enable him to see distant objects clearly? If his least distance of distinct vision without glasses is 3 inches, what would it be

with the above spectacles ? There were few good attempts at the latter part of this question. Q. 7. Describe experiments showing that radiant heat is reflected accord

ing to the same laws as light. The experimental methods suggested were generally too rough. Q. 8. Define dispersive power. What are the conditions that two thin

prisms of different kinds of glass may give when combined, (a)

no dispersion, (6) no deviation ? In many cases dispersion was confused with dispersive power, and the answers were lacking in precision. Q. 9. Explain what is meant by interference of light, and describe a

method by which two separate beams of light from the same

source may be made to interfere. The diagrams given were generally poor, and the appearances presented were often loosely and inaccurately described.

HEAT.

STAGE 2. Results: 1st Class, 21 ; 2nd Class, 123 ; Failed, 48 ; Total, 192. There were comparatively few good papers, about 10 per cent. in all, and rather more than twice as many failures. The majority of the papers were poor in quality. The faults noted seemed in many cases to be due to youth and want of facility of clear expression. Subjoined are special criticisms relating to the several questions. Q. 1. What precautions must be taken, and what corrections applied, to

determine temperatures correctly to 1/100° C. by a mercurial

thermometer between 0° and 100° C. ? Freezing point and boiling point errors (or fundamental interval and one fixed point) should be given, with method of applying correction at inter mediate points. Many candidates omit these, and give a number of less important points without understanding them. Q. 2. Describe a method of measuring the specific heat of a substance

of which only a small quantity can be obtained. What relation has been found between the specific heats of the metallic elements and their atomic weights?

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Bunsen's ice calorimeter, or Joly's steam calorimeter, are the best for this. In the former calorimeter, the tube containing the mercury should not be vertical where the surface of the mercury ends, as the changes of presgure so introduced would effect the melting point of the ice quite appreciably. Round the calorimeter should be an air space and then an ice jacket to protect from radiation. Q. 3. Give a brief historical sketch of the discovery of the first law of

thermodynamics. A historical sketch is asked for. The first law should be given in definite terms—that the heat produced is proportional to the work expended, and not merely that heat appears when work is done. The answer should give a short account of the old caloric theory, and of the experiments connected with the names of Rumford, DavyJoule and Mayer.

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Q. 4. Define what is meant by the dew-point, and show how, when this

is known, the amount of aqueous vapour in the air can be
determined.

What is the weight of a litre of damp air at 20° C., when the
dew-point is 11° C. ? Vapour pressure of water at 11° C.
density of air at 760 mm. and 0° C. = '0013; density of water

vapour = fths that of air.
Relative humidity is not the correct answer to the second part of the
question. The saturation pressure at the dew-point is known, and hence,
knowing the vapour density, the mass can be calculated. The answer is

1.205 grs.

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Q. 5. Enumerate the various ways in which a liquid can lose heat,

distinguishing between the cases in which heat is transformed
into some other form of energy, and those in which no such

transformation takes place.
In radiation, the heat energy is transformed into the energy of ether
waves (until the latter strike some absorbent surface). In evaporation,
part of the heat is used up in doing work against the atmospheric pressure,
and part in doing internal work.
Q. 6. Show how the rise of temperature produced by the adiabatic

compression of a perfect gas can be calculated.

Air at 0° C. is adiabatically compressed to half its volume;

find the rise in temperature. (2* = 8/3 approximately.) First part scarcely attempted. In answering this, the equation pv = RT should be assumed, and also it should be pointed out that the rise of

Work done in compression. temperature of the gas

Note that in an

Sp. Ht. at const. vol. adiabatic expansion the pressure does not remain constant. The answer to the second part is 91° C. Q. 8. What is meant by saying that the internal work done when a gas

expands is small ? Describe experiments which have shown

that the above statement is correct in the case of air. Few understood clearly the meaning of internal work. Q. 9. Explain carefully how the melting point of paraffin wax or sulphur

may be determined by the method of cooling. Observe rate of cooling of a well-stirred mass of paraffin wax. Temperature will remain nearly constant while solidification is going on. There should be no water vessel round the wax while it is cooling, as this will tend to swamp the effect, owing to the increased area of cooling, and increased thermal capacity.

Report on the Examinations in Magnetism and

Electricity

EVENING EXAMINATION.

STAGE 1.

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Results : 1st Class, 709; 2nd Class, 708 ; Failed, 793 ; Total, 2,210. This paper was, on the whole, rather better done than the corresponding paper last year, and this remark applies to each of the three divisions of the paper. Comments on the answers to individual questions are given below.

Magnetism. Q. 1. A wooden ball contains a bar magnet imbedded so that the axis of

the magnet lies along a diameter, but the ends do not reach the surface. Explain carefully how you would mark on the surface of the ball the points where the axis of the magnet prolonged

would cut the surface. Few of the answers were more than partially correct. It was a comnion mistake to float the ball in water, and then to assume the magnet to lie N. and S., and to be horizontal. Various tests (by compass, dip needle, bar magnet, etc.) were suggested, which would only give correct results if the earth's field could be neglected.

Q. 2. What is meant by the statement that the declination at a place is

18° west? At such a place how must a boat be steered by com

pass so that its course may be due east ? Well done on the whole. A curious and not infrequent blunder was to direct the helmsman to steer so that the compass pointed 18° S. of E. Q. 3. A horse-shoe magnet is brought due south of a small compass

needle, the line joining the poles of the magnet being east and west, with the north pole to the west. Describe the manner in which the compass is deflected.

Describe and explain what will happen if the keeper is placed

on the magnet. The drawings were very bad as regards proportions. In the first part the influence of the earth's field was generally ignored. In the second part all the lines of force due to the magnet were regarded as passing through the keeper. Q. 4. How would you hold a rod of soft iron so that the influence of the

earth's magnetic field upon it may be (1) as great as possible, (2)

as small as possible! Frequently well done. For the least magnetic effect almost all placed the rod horizontal, E. and W. Extremely few gave the more general answer, viz., that the rod might be placed anywhere in a plane at right angles to the line of dip.

Frictional Electricity.
Q. 5. Describe and explain the action of a gold-leaf electroscope.

Having charged the instrument positively, how would you test the sign of the charge on the inner coating of a Leyden jar

without discharging or moving either the jar or the electroscope ? Answers to the first part were usually reasonable ; there were scarcely any correct answers to the second. Nearly all the candidates adopted a method by which the jar was partially discharged.

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Q. 6. What is meant by the statement that a given body is at a higher

potential than the earth ? Illustrate your answer by means of

analogous phenomena in heat and hydrostatics. The main part was badly answered. There were two types of answer ; the first omitted to state that it is a flow of positive electricity from a body to the earth that is a test of higher pictential in the former ; the second, whether expressed in terms of two fluids, one fluid or Faraday tubes, merely amounted to saying that a body has higher potential than the earth if it is positively electrified. Q. 7. A hollow metal can is placed on an insulated stand and electrified

Describe the distribution of the electrification on the can and

explain how you would examine the distribution experimentally. Many knew that there is no electrification inside ; not so many stated that the density is greatest at the edges, etc. The statement that the absence of electrification can be proved by connecting the inside to an electroscope was made a good many times ; but a fair proportion knew all about the question. Q. 8. A metal plate A, thickly varnished on the top, is insulated and

connected to a gold-leaf electroscope, the whole being charged with positive electricity until the leaves diverge widely. When another insulated plate B (for instance, the cover of an electrophorus) is placed on the top of A, the divergence of the leaves is very little altered, but if B is touched the leaves fall nearly

vertical. How do you explain these effects ? There was a greater number of unsatisfactory answers to this than to any other question in the paper. The usual mistake was to assume that the touching of B connected the whole apparatus to earth, and allowed the electricity to escape. The common explanation in terms of " free and " bound" electricity was sometimes given, but the number of incorrect explanations in terms of capacity and potential changes was great. Q. 9. Describe and explain the action of a plate-glass frictional machine

How would you use it to charge a Leyden jar? The machine was well described, but the action of the collecting combg seemed to be imperfectly understood. Some attempted to describe the Wimshurst machine, and knew very little about it.

Voltaic Electricity. Q. 10. Describe the Daniell cell, and explain the functions of each part

of the cell and the action that takes place when the poles are connected by a conducting wire.

What advantages does this form of cell possess over a simple voltaic cell consisting of plates of copper and zinc immersed in

dilute acid ? Answered by nearly all, and the best answers were very good.

A large number knew nearly all about the Daniell cell. The function of the porous pot was seldom stated explicitly ; a good many stated that bubbles of hydrogen passed through, and then interacted with the sulphate. Some had very vague notions of polarisation. A few had apparently been taught that copper coated with hydrogen is more electropositive than zirc. Local action was frequently stated to be absent from the Daniell cell, without any mention of amalgamation of the zinc. Q. 11. State Ohm's law, and explain the terms used.

An incandescent electric lamp takes a current of :5 ampère when connected to a circuit of 100 volts. What is the resistance

of the lamp? The answers to this question were too indefinite Nearly ali the candidates stated that current equalled electromotive force divided by resistance, but did not explain themselves by considering any particular case of the

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