which concentrated at a point at unit distance from an equal quantity of the same kind, also concentrated at a point, is repelled with unit force, and taking the charge on each ball as 10 units, find the distance of the balls apart.

[Let x be the half distance between them.

101. What is meant by polarisation of the plates in a Voltaic cell, and what is the cause of the polarisation? Explain how it is got rid of in Daniell's battery.

102. Define unit quantity of electricity on the electro-magnetic C.G.S. (centimetre, gramme, second) system. Taking the ohm to be 109 cms. per second, define Volt, Ampere, and Coulomb.

103. State Faraday's laws of the chemical decomposition of electrolytes. Describe the voltameter, and explain how it can be used for measuring a

current.

104. Find how much zinc is used up per day in each of six cells of a Daniell's battery joined in series and transmitting a current through a total resistance of

D

4 ohms. (One coulomb decomposes 000092 gramme of water atomic weight of zinc-65.) (Electro-motive force of each cell-1.12 volts.)

Therefore quantity of zinc used up per day in each of the six cells

105. Find the work in kilogrammetres done per second by a battery of 80 Daniell's cells (107 volts per cell) sending a current of electricity through an incandescent lamp whose resistance is 65 ohms. The battery is joined in series, and its resistance is. 8 ohms.

106. Taking the data of the preceding question, find how much zinc is consumed per horse power. Taking the cost of sulphate of copper at 21d. per pound, and of zinc at 31d. per pound, find the cost of keeping the lamp lighted for one hour by this means. (One coulomb of electricity decomposes 000092 gramme of water; atomic weight of zinc, 65; of copper, 635; of sulphur, 32; of oxygen, 16. Formula for copper sulphate, CuSO4 + 5H2O.)

[One horse power=76 kilogrammetres.

Zinc used per second

85.6 ·000092 × 2

=80 ×

65

03117 gramine.

2

107. Two cells-one containing CuSO, the other AgNO3--are arranged in series. Find how much sulphate of copper is decomposed and how much copper is deposited in half an hour by a current of 6 amperes, given that 4025 grammes of silver is deposited per ampere per hour.

(Cu" 635; Ag'-108; S"-32; O"=16; N=14.) [Sulphate of copper decomposed

108. Find the resistance of 20 metres of copper wire 0.051 cm. in diameter. Resistance between two

opposite faces of a cubic centimetre of copper is 1,642 x 10-9 B. A. ohms.

[If R, A, L denote resistance, cross section, and length of any wire, then for any two wires

109. Find the work done by a current of 13 amperes flowing through a resistance of 40 ohms (an incandescent lamp). Find how much heat is produced per second in the lamp. (One volt through one ohm of a thermal unit-gramme

generates per second

water-Centigrade.)

1

4.156

[Work per unit time & C2R.

1.3 amperes 13 × 10-1 absolute units of current and 40 ohms=40 × 109 absolute units of resistance, therefore Work in question=(13)2 × 10-2 × 40 × 10o ergs

-67.6 × 107 ergs

HEAT.

110. How did Rumford and Davy disprove the material theory of heat? Describe Joule's apparatus for the friction of water.

111. Describe an arrangement for showing the phenomena of thermo-electric currents discovered by Seebeck. Describe the thermopile.

112. Describe Leslie's experiment of freezing water in a vacuum. Why does water, standing in air, not freeze by its own evaporation?

113. Define critical temperature. Describe the behaviour of carbonic acid gas as to pressure and volume, at temperatures above and below the critical temperature (31°1 C.).

114. Describe Regnault's hygrometer, and explain how to use it.

115. Describe carefully Hope's experiment for finding the maximum density point of water, explaining clearly the principles on which it depends.

A

116. State clearly and briefly the nature of Black's discovery of latent heat of water and of steam. hole is made in a block of ice, and 3 pounds of water at 45° C. is poured into it. How much ice would be

melted if no heat were lost?

[Quantity of ice melted=

3 x 45

79.25

17 pounds.]

117. Prove that if N be the number of degreemeasures in the bulb and stem of a thermometer up to the zero mark (centigrade) and x the rise of the

D2