Maharashtra Board Class 6 Geography Chapter 5 Temperature PDF Download

Temperature

Do It Yourself

Take a torchlight and keep it stable at one place. Take two large paper sheets large enough to accommodate its entire beam. Paste the papers on two flat boards.

Hold the board perpendicular to the beam (figure 5.1A).

Draw the outline of the area lit up by the beam. Name the paper 'A'.

Now use the other paper. Hold it in such a way that it makes an angle of 120° with the beam (figure 5.1B). Draw the outline of the area occupied by the beam. Name the paper 'B'.

Observe both the papers 'A' and 'B'. Now tell:

On which paper does the beam occupy a larger area?

On which paper is the area smaller?

Now change the angle between the beam of light and the paper. Observe the changes that occur in the area occupied by the beam of light.

What is the relation between the angle of the paper and the area occupied by the beam?

Explanation

Sunrays coming towards the earth travel in straight lines. However, as the earth is spherical in shape, these are not perpendicular to all the parts of the earth's surface. In some parts, they are perpendicular whereas in other parts, they are slanting. Let us see what effect it has on the earth.

The perpendicular rays occupy less area (fig 5.1A). The part where the rays occupy lesser area receives bright sunshine and greater heat. Hence the surface there gets heated more and the air becomes hotter.

The slant rays occupy a larger area (figure 5.1B). In this area, sunlight appears less bright and there is less heat. Hence the surface there gets less heated and the air too, is less hot.

Do It Yourself

The region marked 'A' in figure 5.2 receives perpendicular rays, while the region marked 'B' receives slant rays and in the region marked 'C' the rays are extremely slanting.

Using a scale, measure the lengths of the lit up portions on the earth's surface in A, B and C regions.

Measure the width of the rays shown between the earth and the sun.

Considering the parallels of latitude marked in the figure, tell the regions where the temperature will be high, moderate and low.

Discuss this in the class and write the answers in your notebook.

Teacher's Note

The sun gives more heat to the equator because the rays are straight there. In India, the equator passes through Kerala. That is why Kerala is hot all year.

Exam Trick

Remember: Perpendicular rays = small area = more heat. Slanting rays = large area = less heat. This is why the poles are always cold.

Points to Remember

Straight rays hit a small area and give more heat.
Slanting rays hit a large area and give less heat.
The equator gets the most heat from the sun.
The poles get the least heat from the sun.
Temperature decreases as you move away from the equator.

Explanation

Though latitude is the main factor, there are other factors also which influence the distribution of temperature. However, their effects are limited to a particular region. These factors are as follows.

Nearness to the sea, continentality, height above the mean sea-level and physical set-up of a region are factors that lead to diversity in the climate of different regions. Other than these, factors like cloud cover, winds, vegetation cover, urbanization, industrialization, etc. also influence the local climate.

Sunrays falling on the earth are straight and parallel to each other. However, we have seen that due to the spherical shape of the earth and the resultant curvature of the surface, they occupy a larger or lesser area. This leads to unequal distribution of the heat received from the sun, resulting in decreasing temperature from the equator to the North and South Poles. Based on the distribution of temperature, the earth can be divided into torrid, temperate and frigid zones or tropical, temperate and polar regions. Try to understand this from figures 2.4 and 5.3.

Can You Tell

How will the rays fall between 0° and 23°30' North and South?

23°30' and 66°30' North and South?

66°30' and 90° North and South?

Use Your Brain Power

Tell if the following statement is right or wrong. Give reasons. In order to understand the climate of a region, the latitudinal extent is more useful than the longitudinal extent.

Teacher's Note

India is divided into three zones: torrid zone between the equator and 23°30', temperate zone between 23°30' and 66°30', and frigid zone above 66°30'. Our country lies in the torrid and temperate zones.

Exam Trick

Remember the zones: Torrid = hot (like "torrid love"), Temperate = medium temperature (like "temperate weather"), Frigid = very cold (like "frigid ice"). The torrid zone has the most heat.

Points to Remember

The torrid zone is between 0° and 23°30' North and South of the equator.
The temperate zone is between 23°30' and 66°30' North and South.
The frigid zone is between 66°30' and 90° North and South.
Latitude is the most important factor that affects temperature.
Temperature decreases from the equator to the poles.

Do It Yourself

Take two pots of the same size and fill them with water equally. At sunrise, keep one of the pots inside the house and the other one, outside. See that it remains in the sun all the time as shown in figure 5.4 B.

In the afternoon, walk barefoot on the floor inside the house and feel the temperature of the floor. Feel the temperature of the water in the pot inside.

Perform the same activity outside the house and get the feel of the temperature of land and the water kept in the sun. Write down your observations about the temperatures of land and water.

Do this again, around 7 in the evening. Note your observations again. Now you can remove the pots. Discuss all the observations you have noted in the class.

Explanation

You must have realized that the land cools down earlier than the water. The water kept outside in the sun is still a little warm. Due to this difference in the heating and cooling of land and water, the air over the land gets heated faster and also becomes cooler rapidly. The air over the water gets heated slowly and also looses the heat in a slower manner. In the coastal areas, as compared to continental areas, the temperature of air is lower during the day but warmer at night. Contrary to this, the temperature of air in the continental areas is higher during daytime and lower at night.

In the coastal areas, because of the heating of sea water, water vapour gets mixed in the air. This water vapour holds the heat in the air. As a result, the air in the coastal areas remains moist and warm. Conditions in the continental areas are the opposite. As water vapour is absent, the air remains dry. This leads to sharp differences in the day and night temperatures. The difference in the maximum and minimum temperatures of a day is called diurnal range of temperature.

In short, the difference in the day and night temperatures is less in the coastal areas and more in the continental areas. For example, Mumbai temperatures are even, but at Nagpur they vary a lot. In the coastal region of Konkan the range of temperature is less but in Vidarbha, the range of temperature is found to be higher. Therefore, coastal areas have an equable climate whereas in continental areas, the climate is extreme. For example, the climate of Mumbai is equable whereas in continental locations like Nagpur it is extreme. The difference in the mean temperatures of summer and winter is called annual range of temperature.

Always Remember

We normally think that air gets heated due to the sun's rays and because of the hot air, the land and water get heated. But in reality what happens is as follows:

First, land and water get heated due to sunrays. Later, they radiate into the atmosphere, the heat that they have absorbed. As a result, the layer of air close to the surface gets heated. The heat gets transferred vertically to the adjacent upper layers of the air. Hence air closer to the surface is hotter and as one moves higher up from the surface, the temperature of the air decreases. The temperature near the sea-level is higher and it decreases in the mountainous regions.

Teacher's Note

Land and water do not heat the same way. Land heats up fast but cools down fast. Water heats up slowly but cools down slowly. This is why Mumbai near the sea is comfortable all year, but Nagpur inland has very hot summers and cold winters.

Exam Trick

Remember: Land = fast heating, fast cooling. Water = slow heating, slow cooling. Coastal areas have small day-night temperature change. Inland areas have large day-night temperature change.

Points to Remember

Land heats up faster than water during the day.
Land cools down faster than water during the night.
Coastal areas have even temperatures throughout the day.
Inland areas have big differences between day and night temperatures.
Water vapour in coastal air helps keep the temperature steady.

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