Pressure Exerted by Gases Class-8th Goyal Brothers Physics Solutions Chapter-3. We Provide Step by Step Answers of Objective, True False , Fill in the blanks, Match the following , Short/Long Answer Type of Chapter-3,Force and Pressure unit -3(Pressure Exerted by Gases) Visit official Website  for detail information about ICSE Board Class-8.

Pressure Exerted by Gases Class-8th Goyal Brothers

Physics Solutions Ch-3 (unit-3)

 Board ICSE Class 8th Subject Physics Book Name Goyal Brothers Theme-3 Force and Pressure Unit-3 Pressure Exerted by Gases Topic Solution of exercise questions Session 2023-24

OBJECTIVE TYPE QUESTIONS

A. Fill in the blanks :

1. The atmospheric pressure at _sea level_ is 100000 pascals.
2. Mercury is used as a barometric liquid because it is _13.6_ times denser than water.
3. The empty space above mercury in a simple barometer is called _torcellian_ vacuum.
4. Atmospheric pressure can support _10.34_ vertical height of water.
5. The common water pump works on the principle that atmosphere exerts _pressure_.

1. The moisture present in mercury increases the barometric height of simple barometer.

Correct Statement: The moisture present in mercury decreases the barometric height of simple barometer.

2. When the piston of common water pump is raised its piston valve opens.

Correct Statement: When the piston of common water pump is raised its piston valve closed.

3. When the piston of common water pump is lowered its foot valve opens.

Correct Statement: When the piston of common water pump is lowered its foot valve closed.

4. The vertical height of mercury in a simple barometer is dependent on the area of cross-section of barometer tube.

Correct Statement: The vertical height of mercury in a simple barometer is independent on the area of cross-section of barometer tube.

5. Water barometer is possible provided barometer tube is 9 m long.

Correct Statement: Water barometer is impossible provided barometer tube is 9 m long.

C. Write ‘True’ or ‘False’ for the following statements :

1. Aneroid barometer uses pure mercury.[F]
2. The air present can support 13.10m vertical column of mercury.[F]
3. As we go high in t he mountains the atmospheric pressure decreases. [T]
4. A simple barometer is compact and portable. [T]
5. The foot valve of lift pump is placed in the piston. [F]

1. Water is not used as a barometric liquid because:

(a) it is difficult to have a barometer tuber 11m long.

(b) water vaporises under vacuum conditions.

(c) Water sticks to the side of glass tube.

(d) all of the above.

Ans: (d) all of the above.

2. The space above the mercury in a simple barometer is called :

(a) Torcellian vacuum

(b) Newton’s vacuum

(c) Archimede’s vacuum

(d) None of these

Ans: (a) Torcellian vacuum

3. The vertical height of mercury which an simple barometer van support at sea level is :

(a) 76 cm

(b) more than 76 cm

(c) lass than 76 cm

(d) none of these

Ans: (a) 76 cm

4. When the ink foundation pen leaks on high altitude :

(a) pressure of air is more outside than inside the ink pen

(b)pressure of air is lass outside than inside the ink pen

(c) the density of ink on high altitude decreases

(d) none of these

Ans: (b)pressure of air is lass outside than inside the ink pen

4. Aneroid barometer

 Column A Column B 1. A device for lifting groundwater. 3. common water pump 2. A device used to find atmospheric pressure and uses mercury. 1. Mercury barometer 3. A device used to find atmospheric pressure which does not use mercury. 4. Aneroid barometer 4. A valve in the common water pump which does not allow the water to flow back. 2. foot valve

STUDY QUESTIONS

Question 1. What do you understand by the term atmospheric pressure? what is its average value at sea level?

Answer: The atmospheric pressure at a point is defined as the force acting normally on a unit area around that point, due to the total height of the air column of the atmosphere above it. That pressure is known as atmospheric pressure, also known as air pressure. Meteorologists use a metric unit for pressure called a millibar and the average pressure at sea level is 1013.25 millibars.

Question 2. The atmospheric pressure on a hill is 68 cm of mercury. What do you understand from the statement.

Answer: It means that the atmospheric pressure is below normal which is 76 mm Hg.

Question 3. How does atmospheric pressure change with the change in altitude ?

Answer: The atmospheric pressure varies with altitude as density of air decreases as we rise up and air becomes rarer. For example: Pressure at sea level is taken as 76 cm of Mercury Column, which is one atmosphere. For every 105m rise in height, pressure decreases by 1 cm of mercury column

Question 4. Briefly describe construction of a simple barometer.

Answer: A simple barometer can be constructed as follows:

(i) It uses a hard glass tube of length 1m that is closed at one end.

(ii) Fill the tube completely with pure mercury such that no air bubble is present in the tube.

(iii) Seal the open end of the tube with thumb.

Question 5. Why is mercury used as a barometric liquid? Give three reasons.

Answer:  Mercury has high density. Because of this property, when there is a change in pressure the change in height of the mercury in the barometer tube will be very reasonable. Because of this property of mercury, we can measure very high pressure with the help of a barometer while if we use other lower density material, the change in height with pressure will be very high and building such apparatus will be very difficult.

Question 6. Why is not water used as a barometric liquid? Give two reasons.

Answer: Water is not used as a barometric liquid because mercury has a higher density. The atmospheric pressure will support a column of mercury about 30 inches high, while it will support a column of water about 33 feet high. A mercury barometer is therefore more compact and portable than a water barometer.

Question 7. Explain the following:

(a) Why do ink pens start leaking at high altitudes ?

Answer: An ink pens filled with ink contains some air at a pressure equal to atmospheric pressure on earth’s surface. When pen is taken to an altitude, atmospheric pressure is low so the excess pressure inside the rubber tube forces the ink to leak out

(b) Why is hearing affected while going up or coming down from the hill?

Answer: The air pressure outside of your body changes as altitude changes. This creates a difference in pressure on the two sides of the eardrum. You may feel pressure and blockage in the ears as a result.

(c) why does the nose of some people start bleeding when an aeroplane climbs up suddenly?

Answer: With increasing altitude the air pressure decreases, this disturbs the internal and external pressure balance. This disturbance causes the internal body pressure to be more than the outside air pressure. So, as a result of that nose starts to bleed, but this doesn’t happen all the time.

— : end of Pressure Exerted by Gases Class-8th Goyal Brothers :–-