Question

On a hill 1000 m high, the atmospheric pressure will be:

• A. 76 cm of mercury
• B. more than 76 cm of mercury
• C. less than 76 cm of mercury
• D. none of the above

Answer 1

The correct option is C

less than 76 cm of mercury

Explanation of correct option:

option c)

1. The pressure exerted by air due to its weight on the surface of the earth is called atmospheric pressure.
2. Atmospheric pressure at a place is measured by a device called a barometer.
3. It is found that at sea level, the vertical height of mercury supported in the tube is 76 cm above the surface of mercury kept in a bowl.
4. At higher altitudes, the weight of air decreases which decreases the atmospheric pressure at that point.
5. Due to a decrease in pressure, the length of the air column in the barometer decreases.
6. Thus at a height of 1000, the level of mercury in the barometer decreases from its normal value (76cm).

Explanation of incorrect options;

option a)

1. In barometer mercury is used to measure the atmospheric pressure.
2. At sea level, the atmospheric pressure is 76 cm of mercury.

option b)

1. As we move downward in a mine, it is observed that the weight of air increases.
2. With the increase in weight, the pressure exerted by air increases.
3. Thus the level of mercury in the barometer increases from 76cm as we move below the surface of the earth.

Thus, option (c) less than 76 cm of mercury is the correct option.