RBSE Solutions for Class 7 Science Chapter 12 Pressure

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RBSE Solutions for Class 7 Science Chapter 12 Pressure are part of RBSE Solutions for Class 7 Science. Here we have given Rajasthan Board RBSE Class 7 Science Chapter 12 Pressure.

Board RBSE
Textbook SIERT, Rajasthan
Class Class 7
Subject Science
Chapter Chapter 12
Chapter Name Pressure
Number of Questions Solved 63
Category RBSE Solutions

Rajasthan Board RBSE Class 7 Science Chapter 12 Pressure

Text book Exercise

Multiple Choice Questions :

Question 1.
The unit of pressure is :
(a) newton
(b) meter/sec
(c) newton/metre2
(d) joule
Answer:
(c) newton/metre2

Question 2.
As the height of liquid in a column increases, the amount of pressure will be:
(a) Less
(b) More
(c) No change
(d) None of the above
Answer:
(b) More

Question 3.
The spring balance is used to measure:
(a) Work
(b) Weight
(c) Trick
(d) Length
Answer:
(b) Weight

Fill in the blanks :
1. As we move from the earth’s surface to a higher altitude, air pressure will be…………
2. The force acting upon objects immersed in a liquid is called ………..
3. Pascal is unit of ………….
Answer:

  1. Decreasing
  2. Buoyant Force
  3. Pressure

Short Answer Type Question :

Question 1.
Define pressure?
Answer:
Pressure- Vertical force exerted on any contact area is called pressure.
Pressure = Force/area of contact
Pressure is measured in terms of Newton/metre2 or Pascal.

Question 2.
Why is the knife used for cutting vegetable sharper?
Answer:
Since knife is acute shaped, its contact area becomes less. Therefore with less force, more pressure is exerted and hence vegetables are easily cut.

Question 3.
What will be effect on pressure as area increases?
Answer:
With the increase in contact area, pressure gets reduced.

Long Answer Type Questions :

Question 1.
Explain the importance of atmospheric pressure in daily life.
Answer:
Atmospheric pressure affects our daily life in a number of ways.
For example

  1. Diversity in atmospheric pressure on the surface of the earth is responsible for changes in weather.
  2. Low atmospheric pressure is responsible for disasters like storm, tornado, hurricane etc.
  3. Diversity in atmospheric pressure is also responsible for flow of winds on the earth.
  4. Due to less atmospheric pressure on excess heights, mountaineers uses special kind of clothes and artificial respiration systems to save themselves from this low pressure.
  5. With the help of a compressed air, drinking water, taboo water, chemical food etc. is taken from one place to another.
  6. A different musical instrument generates makes different sounds as per the atmospheric pressure.
  7. Compressed gases are used for mechanical speed.
  8. Compressed air is used in the field of mining.
  9. Drinking cold drink with the help of a straw is also possible with the help of atmospheric pressure.
  10. Blood pressure in humans is also affected from Atmospheric Pressure.

Question 2.
What do you mean by buoyant force? The buoyant force is equal to the weight of the displaced liquid, prove it by an experiment.
Answer:
Objects immersed in liquid exerts an upward lifting force, which is known as buoyant force. This quality of liquids is also known as buoyancy.
Buoyant force is equal to the weight of the liquid displaced by an object.
We will explain this with the help of below mentioned activity.
Take a stone. Tie it with a thread with a balance as shown in the picture and measure its weight with the help of its balance scale. Now put this stone in a vessel filled with water. Now measure its weight as (W ), with the help of a pulley. Take out the difference in weight of the stone hanged in air with the stone immersed in water.
RBSE Solutions for Class 7 Science Chapter 12 Pressure 1
Now, as shown in the picture, take water pushed in a measurement glass. Take the weight of this water now. We notice that the weight of the liquid displaced is equal to the difference in weight (When hanged in air-when immersed in water). This measure is equal to the buoyant force. Therefore: Buoyant Force= Weight of the liquid displaced by an object.

Question 3.
Liquids also exert pressure as does air. Explain it.
Answer:
If any vessel filled with water, it exerts pressure on its walls and on bottom of the vessel, it is called liquid pressure. Force exerted on contact area of walls and bottom of the vessel is called pressure of the liquid.

Activity
Activity 1: (Page-114)

Place 2 books on your palm.
Question 1.
What do you feel?
Answer:
We experience a force on the palm. Now remove one book.

Question 2.
What difference do you feel now in the to previous position?
Answer:
Less force is exerted as compared to previous, when one book is removed.

Question 3.
Why do you feel more comfort able in second situation then previous one?
Answer:
Due to less force exerted in second situation, pressure exerted is also less. Hence we feel comfortable in the second situation.
In first situation, due to more exertion of force, more pressure is exerted.

Activity 2: (Page-115)

Question 1.
Why does nail penetrate into wooden block this time?
Answer:
When nail is hammered with great force, more pressure gets exerted, hence nail penetrates into the wooden block easily this time.

Question 2.
Why pointed nail gets into the wooden block easily, as compared to a thicker nail?
Answer:
The area of a pointed nail is less in comparison to a thicker nail. Therefore when equal force is exerted, pointed nail exerts more pressure and hence gets (penetrates) into the wooden block easily. On the basis of above two experiments, it is proved that pressure applied on any object depends on force.

Activity 3: (Page-115)

Question 1.
In which situation balloon punctured easily?
Answer:
Since pointed pin has a less area in comparison to the area of the bottom edge of the pin, Therefore when applying equal force with both, more pressure gets exerted with a pointed pin. Therefore it was more easy to burst a balloon with a pointed end of the pin.

Activity 4: (Page-115)

Question 1.
In which situation, contact area of the brick and the sponge is less?
Answer:
When brick input vertical on the sponge, contact area of both is less.

Question 2.
Why sponge gets more depressed when brick is made to stand on it?
Answer:
When a brick is made to stand on the sponge, contact area gets decreased, hence more pressure is exerted on the sponge. Therefore it gets more depressed.

Activity 5: (Page-116)

Question 1.
What do you see?
Answer:
Bottle gets compressed.

Question 2.
Why bottle gets compressed?
Answer:
When we empty hot water, water vapors get filled inside the bottle. When cold water is put on the bottle, these water vapors cool down and become liquid, which leads to decrease in pressure inside the bottle, due to pressure of air outside, bottle gets compressed. Therefore, we can say that air exerts pressure.

Activity 6: (Page-116)

Question 1.
Why volume inside the balloon start increasing with the increase of water?
Answer:
Liquid exerts pressure in all directions, henceforth, volume of the balloon also increases.

Question 2.
Why balloon gets burst when liquid level increases?
Answer:
When water increases inside the balloon, it starts applying more pressure. When balloon is not able to stand this increased amount of pressure, it gets burst.

Activity 7: (Page-117)

Question 1.
What is the effect on pressure of the liquid, when height of the water column is increased?
Ans:
With the increase in height of the water column, pressure also gets increased.

Activity 8: (Page-118)

Question 1.
What is the liquid pressure on points placed on the same horizontal area?
Answer:
Liquid exerts same pressure on all the points placed on a horizontal area.

Question 2.
What will be the liquid pressure on points placed at different heights?
Answer:
Liquid exerts different amount of pressure on the points placed on different heights.

Activity 9: (Page-118)

Question 1.
From which hole, water flows at a far distance?
Answer:
From hole C, water flows at a far distance.

Question 2.
Why does water flows at a far distance from hole C?’
Answer:
Due to increased amount of pressure, water flows at a far distance from hole C.

Question 3.
Why does water flow at a near distance from hole A?
Answer:
Pressure exerted is minimum in hole A, hence water flows at a near distance.

Activity 10: (Page-119)

Question 1.
What do you experience?
Answer:
While holding the stone, still in water, its weight appear to be less.

Question 2.
Why stone appears to weigh less when immersed in water?
Answer:
When stone is dipped in water, an upward bounce force is exerted, hence stone appears to weigh less.

Question 3.
What do you call an upward force exerted on any object, when in water?
Answer:
Buoyant Force.

Question 4.
What do you call the buoyant force exerted by the liquid?
Answer:
Buoyancy.

Activity 11: (Page-120)

Question 1.
Why is difference observed in weight, when an object is dipped in water?
Answer:
Liquid exerts an upward buoyant force on an object dipped in it, hence object appears to weigh less when in water.

Question 2.
Less weight of an object is equal to?
Answer:
Less weight of an object is equal to the weight of a liquid displaced by an object.

Question 3.
What is the principle called, which is described as per above experiment?
Answer:
This principle is known as Archimedes principle.

Other Important Questions

Multiple Choice Questions :

Question 1.
What is the relation between force (F), pressure (P) and area (A).
(a) P=F/A
(b) A=FP
(c) F=AP
(d) F2=PA
Answer:
(a) P=F/A

Question 2.
Newton/metre2 is known as
(a) Weber
(b) Ferade
(c) Pascal
(d) None of these
Answer:
(c) Pascal

Question 3.
What is the average atmospheric pressure at the sea level?
(a) 100 pascal
(b) 1000 pascal
(c) 10000 pascal
(d) 101325 pascal
Answer:
(d) 101325 pascal

Question 4.
What is the machine called used to measure atmospheric pressure?
(a) Hydrometer
(b) Barometer
(c) Hygrometer
(d) None of the above
Answer:
(b) Barometer

Fill in the blanks
1. Pressure value of any object depends on contact …………. of the object on which pressure is exerted.
2. Air exerts same amount of pressure in all……
3. Pressure of liquid on one point is …………….situated on same horizontal area.
4. With increase in depth, pressure of liquid
Answer:

  1. area
  2. directions
  3. equal
  4. increases.

Very Short Answer Questions

Question 1.
How is pressure measured?
Answer:
Pressure of the liquid is measured in Newton/meter or pascal.

Question 2.
On what aspects does the pressure exert on any object depend?
Answer:
Pressure exerted on any object depends on force exerted and its contact area.

Question 3.
What is air pressure?
Answer:
Amount of pressure exerted by air on 1 square meter of an area, is known as air pressure.

Question 4.
What is called Atmospheric Pressure?
Answer:
Pressure exerted by atmosphere, surrounded in all directions, is known as atmospheric pressure.

Question 5.
What is the average atmospheric pressure at the sea level?
Answer:
101325 Pascal.

Question 6.
What is the impact on pressure if height of water column increases?
Answer:
With the increase in height of water column, pressure of the liquid also increases.

Question 7.
What is the pressure exerted on the points situated on the same horizontal area?
Answer:
Pressure exerted is same for all points situated on same horizontal area.

Question 8.
Water exerts what kind of force on the object immersed in it?
Answer:
Water exerts Buoyant force on the object immersed in it.

Question 9.
Buoyant force is equal to what aspect?
Answer:
Buoyant force is equal to weight of the liquid displaced by an object.

Short Answer Type Questions

Question 1.
We cannot walk with ease in desert as camel does. Why?
Answer:
The contact area of our foot base is less, hence our body weight comes on our foot, due to which pressure increases so much that our foot start getting inside the sand. That is why we face difficulty in walking in desert. Feet of the camel are spongy and are broad. Due to more contact area, pressure exerted is less; hence foot of the camel does not get inside the sand. Therefore camel walks easily in sand.

Question 2.
Why walls of the dam are made thick from bottom and thin-from above?
Answer:
Pressure on any point inside the liquid increases with the increase in depth of the free surface. Since dams are very deep, pressure on . the bottom surface of the dam is maximum. That is why walls of the dam are made thick from the bottom. When water travels upwards, pressure start decreasing, hence walls are made thin on above areas of a dam.

Question 3.
Why do sheets and tiles of houses get shattered with the storm?
Answer:
When storm comes, air pressure on roof top decreases whereas air pressure inside the room increases. That is why tiles and sheets of roof
top gets shattered when storm comes.

Question 4.
When traveling in heights, why do we face difficulty in breathing as height increases?
Answer:
With the increase in height, respective atmospheric pressure starts decreasing. Due to less atmospheric pressure, we face difficulty in breathing. Also, oxygen gets reduced when we travel to greater heights, that is why mountaineers carry oxygen cylinders with them.

Question 5.
Why are water tanks kept at heights for distribution of water?
Answer:
For supply of water in houses made at heights, it is necessary that water sent for distribution should flow with more pressure and also, height of the water tank should be more than the height of the house. Therefore for distribution of water, water tanks are made at heights.

Question 6.
What is the difference between force and Pressure.
Answer:

Force Pressure
1. Force is that factor which brings changes in state of an object, or try to bring change in its state. 1. Vertical force exerted on an area is called pressure.
2. Force exerted does not depend on the contact area of an object. 2. Pressure exerted depends on the contact area of an object.
3. Force is measured in Newton. 3. Pressure is measured in newton/m2.

Question 7.
What are the principles of liquid pressure?
Answer:
Principles of liquid pressure are as mentioned below:

  1. In still water, same pressure is exerted on all the points lying in same horizontal area.
  2. Inside still water, on any point,pressure exerted in each direction is same.
  3. With the increase in water column, its pressure also increases.
  4. if pressure is exerted on any point of the liquid, it gets distributed equally in water.

Question 8.
Explain Archimedes Principle.
Answer:
According to Archimedes principle: Difference in weight of an object is observed when immersed in water partially or completely, and this difference in weight is equal to the water displaced by an object.
Difference in weight of an object= Weight of the liquid displaced by an object.

Long Answer Type Questions

Question 1.
Explain reasons of below mentioned

  1. Our body experience high amount of atmospheric pressure, still our body does not get puckered.
  2. Why are strips of the school bags made thicker and broad.
  3. Tyres of heavy vehicles Eire made very thick
  4. Divers wear a metal armor while diving in sea.

Answer:

  1. Air of atmosphere exerts so much pressure on human body that it experiences approx. 15000 kg of weight force still our body does not get puckered, because pressure in our body balances the air pressure.
  2. Strips of school bags hanged on shoulders are made thick, so that their contact area gets increased and therefore pressure exerted on the shoulder becomes less, and bags can be carried easily by children on their shoulders.
  3. Pressure exerted on roads or land, is expressed by the ratio of force and contact area of the same. Due to thickness of tyres, contact area gets increased, therefore pressure exerted on roads/land becomes less. Therefore due to less pressure, tyre does not get inside the mud on the road and vehicle moves easily.
  4. When you go deep inside the water, pressure increases. Therefore body of the divers will not able to stand with pressure when they go deep inside the sea. With the help of a metal armor, pressure gets exerted on this metal shield rather than on body of the diver. Hence divers can easily go inside the sea.

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