PRESSURE
1. What is pressure? Write its S.I. unit.
-Pressure is a perpendicular force acting on per unit area. It's S.I unit is pascal.
2. Define 1 pascal pressure.
- One pascal pressure is defined as one newton of force applied on the surface area of one meter square.
3. All cutting instrument has sharp edges, why?
- We know, P=F/A
which means pressure is inversely proportional to the surface area if force is kept constant.So, the sharp edges has small surface area and are capable of exerting more pressure due to it which makes cutting easier. Hence, they have sharp edges.
4. Define liquid pressure and derive p=hdg.
- The force exerted by liquid on per unit area of the wall of the container is called liquid pressure.
5. List the factors on which liquid pressure depends.
-The factor on which liquid pressure depends are:
a. Depth of the liquid. (h)
b. Density of the liquid.(d)
c. Acceleration due to gravity.(g)
6. List the laws of liquid pressure.
- The laws of liquid pressure are:
a. Liquid find it's own level.
b. Pressure applied on an enclosed liquid transmits equally in all direction.
c. Liquid pressure is directly proportional to the depth of the liquid.
d. Liquid pressure depends on its density
7. Why are dams made wider at the base?
- Since, P=hdg. It is clear that more the depth of the liquid more will be the pressure. Hence, to withstand the enormous amount of pressure the dams are made wider at the base.
# SIMILAR ANS TO THE FOLLOWING QUESTION.
*Deep sea divers use swim suit, why?
* A bucket at ground floor fills faster than at the top floor, why?
8. State pascals law and instrument based on it.
- It state that"the pressure exerted in any part of enclosed fluid transmits equally and perpendicularly to all the other part of the fluid."
Instruments based on it are:
Hydraulic lift, Hydraulic press, Hydraulic brakes e.t.c.
9. Explain the working principle of hydraulic machines.
- Let F1 and F2 be the force applied in small and big piston respectively and A1 and A2 be their respective surface area. Hence, we know from pascals law ,
Since, A2 is greater than A1, F2 will be greater than F1. It shows that the force is multiplied.
10. What are the reason for using liquid in a hydraulic lift?
- The reasons for using liquid in a hydraulic lift are:
a. Liquid transmits pressure equally in all direction.
b. Liquid's volume cannot be changed by compressing.
11. Define upthrust or buoyancy with it's unit. In which direction does it act?
- Upthrust is defined as the resultant upward force experienced by an object when immersed partially or wholly. It's S.I unit is Newton. It acts in the direction opposite to the direction of gravity (Upward).
12. Write the factors on which upthrust depends.
- Since, U= vdg. It is clear that upthrust depends on following factors:
a. Volume of displaced liquid (v).
b. Density of the liquid(d).
c. Acceleration due to gravity(g).
12. Write the relationship between density of liquid and upthrust.
- The upthrust is directly proportional to the density of the liquid.
Note- Therefore salty water provides greater upthrust than pure water and egg float on salty water.
13. Define density and relative density with its unit.
- The total amount of mass present per unit volume is called density. It's unit is kg per meter cube.
Mathematically, d=m/v.
- Relative density is defined as the ratio of density of the substance to that of density of water at 4°c.It has no unit.
Mathematically,
R.D=density of substance/density of water at 4°c.
14. State Archimedes principle.
-Archimedes principle states that,"when an object is wholly or partially immersed into a liquid, it experiences an upthrust which is equal to the weight of the displaced liquid".
15. Where does an object has less weight in air or in liquid?
- An object has less weight in liquid because liquid exerts more upthrust than air.
16. State law of floatation.
- Law of floatation states that," Every floating object displaces liquid equal to its own weight".
Note- Ship floats on water because it displaces liquid equal to it's own weight and due to its hollow body, it's density is less than that of water.
Iron nail sinks in water because it cannot displace liquid equal to its own weight and has more density than water.
17. What are the application of law of floatation?
- The application of law of floatation are:
a. To make a hydrometer.
b. To make a ship.
18. What is hydrometer? Give an example.
- A hydrometer is a device which is used to measure the density and relative density of various liquid and it is based on law of floatation. For example- lactometer is used to measure the purity (density)of the milk.
19. Define atmosphere.
- The mixture of different gases, dust particles, sand, water vapour etc. Which is present around the earth's surface is call atmosphere.
20. Define atmospheric pressure and it's value at the sea level.
- The force applied by the mixture of air on a unit surface area of the earth is called atmospheric pressure.
It's value at sea level is 760 mm of Hg or 10^6 pascal.
21. What are the application of atmospheric pressure?
- The application of atmospheric pressure are-
We cal fill ink in a fountain pen, medicine in a syringe, to draw water using water pump etc.
22. What is a Barometer? Write its working.
-It is the instrument use to measure the atmospheric pressure.
Working- Inside a barometer, there is some vacuum just above the mercury level which is called Toricellian vacuum. When atmospheric pressure decreases, the level of mercury in a barometer decreases and when the atmospheric pressure increases, the level of mercury increases.
23. Define syringe and it's working.
- A syringe is a medical instrument which is used to take out blood from our body or inject medicine.
Working: A syringe consist of a needle, nozzle, piston and a cylindrical body. When a piston is pulled a vacuum is created inside the body and the medicine from a bottle enters it, when the piston is pushed the pressure inside the syringe becomes more than that of our body and hence the medicine enters our body through needle.
24. Define air pump with working.
- It is an instrument which is used to fill air in the tubes of tyres .
Working- It consist of a nozzle,cylindrical body and a piston. When the piston is pulled the air enters the cylindrical body as the atmospheric pressure is more than that of pressure inside the pump. When the piston is pulled the pressure inside the pump becomes more than the pressure of tube and hence air enters the tube.
Note- Pressure gauge measures the pressure in the tubes of Tyre.
25. Define hand pump and it's working.
- It is an instrument used to draw the water from under ground.
Working: It consist of move able valve and barrel valve,handle, cylindrical body, outlet and a piston.
There are two processes;
a. Upstroke- When the handle is pushed, the piston comes up and vacuum is created between barrel valve and move able valve. Due to low pressure move able valve gets closed and water rises through barrel valve. Hence, pushing down of handle to rise up the piston is called upstroke.
b. Down stroke- When handle is pulled, the piston moves down and move able valve opens and barrel valve closes. Since both valves comes closer the pressure between them increases and the water rises up through movable valve. So, pulling up of the handle to push down the piston is called down stroke.
26. Why does the helium filled balloon rises and then halts?
- The density of helium is less than air. So, due to the upthrust of air it rises up. When the density of air equals to density of helium it halts.
27. Which instrument measures the blood pressure of human body?
- Sphygmomanometer is the instrument used to measure the blood pressure of human body.
12. Write the relationship between density of liquid and upthrust.
- The upthrust is directly proportional to the density of the liquid.
Note- Therefore salty water provides greater upthrust than pure water and egg float on salty water.
13. Define density and relative density with its unit.
- The total amount of mass present per unit volume is called density. It's unit is kg per meter cube.
Mathematically, d=m/v.
- Relative density is defined as the ratio of density of the substance to that of density of water at 4°c.It has no unit.
Mathematically,
R.D=density of substance/density of water at 4°c.
14. State Archimedes principle.
-Archimedes principle states that,"when an object is wholly or partially immersed into a liquid, it experiences an upthrust which is equal to the weight of the displaced liquid".
15. Where does an object has less weight in air or in liquid?
- An object has less weight in liquid because liquid exerts more upthrust than air.
16. State law of floatation.
- Law of floatation states that," Every floating object displaces liquid equal to its own weight".
Note- Ship floats on water because it displaces liquid equal to it's own weight and due to its hollow body, it's density is less than that of water.
Iron nail sinks in water because it cannot displace liquid equal to its own weight and has more density than water.
17. What are the application of law of floatation?
- The application of law of floatation are:
a. To make a hydrometer.
b. To make a ship.
18. What is hydrometer? Give an example.
- A hydrometer is a device which is used to measure the density and relative density of various liquid and it is based on law of floatation. For example- lactometer is used to measure the purity (density)of the milk.
19. Define atmosphere.
- The mixture of different gases, dust particles, sand, water vapour etc. Which is present around the earth's surface is call atmosphere.
20. Define atmospheric pressure and it's value at the sea level.
- The force applied by the mixture of air on a unit surface area of the earth is called atmospheric pressure.
It's value at sea level is 760 mm of Hg or 10^6 pascal.
21. What are the application of atmospheric pressure?
- The application of atmospheric pressure are-
We cal fill ink in a fountain pen, medicine in a syringe, to draw water using water pump etc.
22. What is a Barometer? Write its working.
-It is the instrument use to measure the atmospheric pressure.
Working- Inside a barometer, there is some vacuum just above the mercury level which is called Toricellian vacuum. When atmospheric pressure decreases, the level of mercury in a barometer decreases and when the atmospheric pressure increases, the level of mercury increases.
23. Define syringe and it's working.
- A syringe is a medical instrument which is used to take out blood from our body or inject medicine.
Working: A syringe consist of a needle, nozzle, piston and a cylindrical body. When a piston is pulled a vacuum is created inside the body and the medicine from a bottle enters it, when the piston is pushed the pressure inside the syringe becomes more than that of our body and hence the medicine enters our body through needle.
24. Define air pump with working.
- It is an instrument which is used to fill air in the tubes of tyres .
Working- It consist of a nozzle,cylindrical body and a piston. When the piston is pulled the air enters the cylindrical body as the atmospheric pressure is more than that of pressure inside the pump. When the piston is pulled the pressure inside the pump becomes more than the pressure of tube and hence air enters the tube.
Note- Pressure gauge measures the pressure in the tubes of Tyre.
25. Define hand pump and it's working.
- It is an instrument used to draw the water from under ground.
Working: It consist of move able valve and barrel valve,handle, cylindrical body, outlet and a piston.
There are two processes;
a. Upstroke- When the handle is pushed, the piston comes up and vacuum is created between barrel valve and move able valve. Due to low pressure move able valve gets closed and water rises through barrel valve. Hence, pushing down of handle to rise up the piston is called upstroke.
b. Down stroke- When handle is pulled, the piston moves down and move able valve opens and barrel valve closes. Since both valves comes closer the pressure between them increases and the water rises up through movable valve. So, pulling up of the handle to push down the piston is called down stroke.
26. Why does the helium filled balloon rises and then halts?
- The density of helium is less than air. So, due to the upthrust of air it rises up. When the density of air equals to density of helium it halts.
27. Which instrument measures the blood pressure of human body?
- Sphygmomanometer is the instrument used to measure the blood pressure of human body.
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