Page 590 - SUBSEC October 2017_Neat

PRACTICAL ACTIVITIES (cont’d)

It is important that you take care in setting up the apparatus: if the incident ray does not go through
the centre of the circle then the refracted ray will bend again at the curved surface.

Plot a graph of β against α and extend the graph to find the value of β when α is 90°.

Also plot a linear graph with the same data and obtain a second value for the critical angle.

In your summary comment on the relative merits of the two alternative ways of handling the data.

LATENT HEAT

Refer to Unit 1, Module 3, Specific Objective 2.7

Aim: To determine:

(i) the specific latent heat of vaporisation of a liquid by an electrical method: and

(ii) the specific latent heat of fusion of ice by the method of mixtures.

Method: (a) The more sophisticated apparatus in the text may not be available, in which case the
apparatus shown below can be used. The principle is the same. The energy supplied
after the liquid has started to boil is equal to the heat required to boil off a mass n of
liquid plus the heat to the surroundings, H, that is, Vlt = mL+H.

If the procedure is repeated with different values of V and I but with the same time, t, then the last
term may be eliminated by subtraction. (Explain why the heat loss is the same in both cases, provided
the time is the same).

CXC A16/U2/17 90