1. Distinguish between diurnal and annual ranges of temperature.

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What do you mean by diurnal range of temperature and annual range of temperature?

The difference between the maximum and the minimum temperatures of a day is known as the diurnal range of temperature.

The difference between the maximum and the minimum temperatures recorded in a year is known as the annual range of temperature.

2. Distinguish between weather and climate.

(i) Weather is hour-to-hour, day-to-day condition of the atmosphere. It can change dramatically from day-to-day. On the other hand, climate refers to the average weather conditions of a large area over a long period of time.

(ii) The change of weather is a continuous phenomenon. It is never constant. On the contrary, the climate of a place is permanent in nature. It remains more or less the same year after year.

3. What is weather forecast?

(i) Name the various media through which we receive weather forecast.

(ii) How is it useful for us?

(i) Predictions about weather are announced by the weather stations on a daily basis. These predictions are collectively called weather forecast.

(ii) We receive weather forecast through newspaper, television and radio.

(iii) Weather forecast gives us advance warning of cyclones, floods, droughts, etc. Thus, it makes us alert enough to the catastrophic events more wisely. Weather forecast reduces the chances of extreme situations.

4. Distinguish between absolute humidity and relative humidity.

Absolute humidity refers to the actual amount of water vapour in a given volume of air at a given temperature. It is measured in grams per cubic metre. Relative humidity refers to the ratio between the actual amount of water vapour present in the air at a given temperature and the maximum capacity of the air to hold moisture at the same temperature. It is always expressed in percentage.

5. What are the features of cumulus clouds?

(i) They are found between 2000 m and 6000 m of altitude.

(ii) They are medium clouds and have fibrous structure.

(iii) They are dense clouds with watery appearance.

(iv) They bring showers.

6. What are the various forms of precipitation?

Precipitation comes down to the earth in various forms-rains, drizzle, snow, sleet and hail.

(i) Rain: When precipitation comes down to the earth in the form of water drops it is called rain.

(ii) Drizzle: When the drops of rain are very small it is called drizzle.

(iii) Snow: When the temperature of the air is below freezing point, the condensation takes place in the form of small crystals of ice. They combine together and fall on the earth as snow.

(iv) Sleet: Sometimes snow and rain fall together which we call sleet.

(v) Hail: It is the solid form of precipitation. It consists of balls or irregular lumps of ice, each of which is called a hailstone.

7. What are the various forms of condensation?

The various forms of condensation are - clouds, dew, frost and fog.

(i) Clouds: They are formed when the moisture in the air condenses at high altitude. It is the most important form of condensation.

(ii) Dew: It is formed when the moisture in the air comes in contact with cold surface.

(iii) Frost: It is formed when dew occurs in the form of ice crystals.

(iv) Fog: It is formed when the moisture in the air condenses very close to the land surface or above the water bodies.

8. Why is rain gauge installed in the open space.

Rain gauge is installed in the open space, away from trees or buildings so that extra water does not get collected.

9. What does 'a centimetre of rainfall' mean?

'A centimetre of rainfall' means the amount of water that would cover the ground to a depth of one centimetre, if it does not drain off or evaporates.

10. Why are alcohol and mercury the commonly used liquids in thermometers?

It is because, these liquids have the property of expanding and contracting with the rise and fall of the temperature. This is recorded in glass tubes which are graduated.

11. How is wind direction measured with the help of wind vane?

Wind vane is the instrument used to record the direction from which wind is blowing. A rod with a pointer and a tail is fixed on either end of a horizontal rod. The pointer shows the direction from which the wind is blowing and the tail or vane is on the side towards which the wind is blowing. This instrument (wind vane) is installed away from tall trees or buildings so that natural direction of wind can be measured.

12. Give a brief description of Beanfort Scale.

The full name of Beanfort Scale is Beanfort Wind Force Scale. It was derived by Sir Francis Beanfort of the British Navy in 1805  to help sailors at sea. This scale is used to measure wind velocity (strength) based on the observed sea conditions. It was originally based on the effect of wind speed on sailing ships. There are 13 levels of wind strength from 0 to 12 on this scale. These levels range from dead calm to deadly hurricane. This scale is still in used today and has been adapted for use on land.

13. What do you mean by low pressure and high pressure?

The unit of measurement of pressure is millibars (mb). The normal pressure at sea level is 1013 mb. When pressure is less than 1013 mb it is called low pressure. When it is more than 1013 mb it is called high pressure.

14. Give an account of different types of clouds.

Depending on the shape, appearance and height at which clouds are formed, they are classified into four groups - cirrus, cumulus, stratus and nimbus.

(i) Cirrus clouds: They are high clouds found between 6000 m and 12000 m of altitude. They contain small crystals of ice and have curly hair-like appearance. They do not bring rain.

(ii) Cumulus clouds: They are medium clouds found between 2000 m and 6000 m of altitude. They have fibrous structure. They are dense clouds with watery appearance. They bring sharp showers.

(iii) Stratus clouds: They are low clouds found above 2000 m of altitude. They are uniformly dull and dark grey in colour. They spread like a sheet. They bring drizzle.

(iv) Nimbus clouds: They are real rain-bearing clouds. They are found below 2000 m of altitude. They are thick and dark. They spread out in layers and bring rain or snow.

15. What is atmospheric pressure? How is it measured by aneroid barometer?

Atmospheric pressure is the pressure exerted by the weight of air on the earth's surface. As we go up the layers of atmosphere, the pressure falls rapidly. The air pressure is maximum at the sea level and decreases  with height.

The instrument used to measure atmospheric pressure is called barometer which is of two types - mercury barometer and aneroid barometer. Aneroid barometer is more commonly used though it is not as accurate as the mercury barometer is.

Aneroid barometer is a metal box which is partially vacuum. The box is very sensitive to variations in air pressure. It expands in low pressure and gets compressed in high pressure. There is a pointer connected to this box which over a scale to indicate atmospheric pressure. Aneroid barometer is used in a barograph also to have a continuous record of pressure changes.