1. SSS TWO PHYSICS FIRST TERM
DEFINITION OF TERMS

2. Boiling point of a substance is defined as the temperature at which its saturated vapour pressure becomes equal to the external atmospheric pressure
Relative humidity is the ratio of the mass of water vapour in a given volume of air to the mass of water vapour required to saturate the same volume of air at the same temperature. It is expressed in percent. It is measured with a hygrometer. It is used by weathermen for making weather forecast.
Evaporation is the escape of water molecules into the atmosphere from a water contained body. It causes cooling.

3. Factors affecting evaporation
Temperature
Surface
Wind
Humidity/dryness of air
Pressure
Nature of liquid/viscosity/density

4. Factors affecting boiling point of a liquid
Nature of the liquid
External atmospheric pressure
Presence of impurities
Degree of its molecular cohesive force
N/B
The extra heat giving to boiling water is not to increase the temperature but to break the intermolecular forces in the molecules of water.

5. Differences between boiling and evaporation
This is the change from liquid to vapour at temperature below normal boiling point.
Takes place slowly at the liquid surface.
Takes place at all temperatures.
This is the change from liquid to vapour at the boiling point.
Occurs throughout the entire volume of the liquid.
Takes place at a particular temperature.

6. Differences between boiling and evaporation
Temperature needs not be steady during evaporation.
Wind assists evaporation.
Temperature remains steady during boiling.
Wind has no effect on boiling.

7. The similarity between evaporation and boiling is that both involve liquid phenomenon.

8. Assignments
The mass of water vapour in a given volume of air at 20 degree Celsius is 0.05g. The air requires 0.15g of water vapour to saturate it at the same temperature. Calculate the relative humidity of the air.
Describe an experiment to show that evaporation causes cooling.

9. ( Take specific heat capacity of the soup = 4000J/kgK)
Define heat capacity and state its unit.
A quantity of pepper soup of mass 800g poured into a plastic container with a tight fitting lid has a temperature of 30 degree Celsius. The container is then placed in a microwave oven, rated 1200W and operated for 3minutes.
Calculate the final temperature attained by the soup. (Assuming no heat losses).
Explain why containers with tight-fitting lids are not suitable for use in microwave cooking.
When the soup is brought out and allowed to cool, a dent is observed on the container. Explain.
( Take specific heat capacity of the soup = 4000J/kgK)