Question 9
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(a) Define each of the following terms:
(i) humidity;
(ii) saturated vapour.
(b) Explain each of the following observations:
(i) steam at 100o C causes more severe burns than water at 100o C;
(ii) water pipes sometimes burst during very cold weather.(c) State two differences between heat and temperature:
(d) A simple pendulum has a period of 4.2 s. When its length is shortened by 1 m, the period becomes 3.7 s. Calculate the:
(i) original length of the pendulum;
(ii) acceleration due to gravity. [Take π = 3.142]
Observation
Part (a) Well attempted by most candidates.
Part (b) Many candidates attempted this question correctly.
Part (c) Candidates performance was average.
Part (d) Candidates performance was below average.
The expected answer is:
9.
(a)
(i) Effects of heat on substances
- Increase in temperature
- Thermal expansion
- Decrease in resistance of semiconductors
- Change of state
- Thermionic emission
- Increase in resistance of metals
- Reduction in viscosity of liquids
- Increase in viscosity of gases
(ii) Explanation of statement ‘the specific latent heat of fusion of ice
is 3.34 x 105 J kg-1
It means that the quantity of heat required to change
1 kg of ice at 0 °C to water at 0 °C is 3.34 x 105 J
(b) Calculation of required mass of water
Let the quantity of heat required to melt 0.02 kg of ice and raise the temperature to 35 °C be Q1
then,
The quantity of heat required to increase the temperature of water from 35°C to 35 °C = Q2
then;
Heat lost by steam in condensing at 100 °C and thereafter cooling to 35 °C = Q3
Assuming no heat was lost to the surrounding,
Total mass of water in container = mass of condensed steam + mass of melted ice + mass of water originally in the container
= 8.636 x 10-3 + 0.02 + 0.3
= 0.328636 kg