Matric Notes Physics 9th Ch 7 Properties of Matter Long Questions
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Answer: Matter has three states solids, liquid and gases. These three sates of matter are explained not he basis of kinetic molecular theory. It is assumed that:
Solids:
1. Solids are made up of molecules which are arranged closely in a fixed pattern.
2. Molecules in solids vibrate about their mean position.
3. The attractive forces between the molecules are strong.
1. Solids are made up of molecules which are arranged closely in a fixed pattern.
2. Molecules in solids vibrate about their mean position.
3. The attractive forces between the molecules are strong.
Liquids:
1. Liquids are also made up of molecules which are close together.
2. The pattern of molecules is not fixed and does not extend far. The molecules in a pattern keep changing their position.
3. Molecules are able to move about, which means that a liquid is able to change its shape and can adopt the shape of the container.
4. The attractive forces between the molecules of liquid is less than the solid.
1. Liquids are also made up of molecules which are close together.
2. The pattern of molecules is not fixed and does not extend far. The molecules in a pattern keep changing their position.
3. Molecules are able to move about, which means that a liquid is able to change its shape and can adopt the shape of the container.
4. The attractive forces between the molecules of liquid is less than the solid.
Gases:
1. A gas is made up of molecules which are in constant random motion.
2. The distance between molecules id larger as compared to the size of molecules.
3. The molecules are constantly colliding elastically with each other and with the walls of the container.
4. Forces between molecules are negligible, except during collisions.
Q.2) Define and explain density and pressure.
Answer: Density:
“Mass per unit volume of a body is called density”. It is a scalar quantity.
Let’s take the example of iron and wood. The same volume of iron is heavier than wood due to the reason that the density of iron is more than that of wood. In other words, the mass of iron for 1 m3 is more than the mass of wood of 1 m3 volume.
Molecules of iron are held closely together, whereas the molecules of wood are arranged in a different manner and have voids in the structure so the number of molecules in the same volume is more in case of iron than the wood.
1. A gas is made up of molecules which are in constant random motion.
2. The distance between molecules id larger as compared to the size of molecules.
3. The molecules are constantly colliding elastically with each other and with the walls of the container.
4. Forces between molecules are negligible, except during collisions.
Q.2) Define and explain density and pressure.
Answer: Density:
“Mass per unit volume of a body is called density”. It is a scalar quantity.
Consider a body of mass ‘m’ has a volume ‘v’. The density of an object is; 
Explanation:Let’s take the example of iron and wood. The same volume of iron is heavier than wood due to the reason that the density of iron is more than that of wood. In other words, the mass of iron for 1 m3 is more than the mass of wood of 1 m3 volume.
Molecules of iron are held closely together, whereas the molecules of wood are arranged in a different manner and have voids in the structure so the number of molecules in the same volume is more in case of iron than the wood.
Pressure:
“The normal force applied per unit area is called pressure”. It is denoted by “P”.
Mathematically:
The SI unit of pressure is pascal (Pa).
Pascal:
It can be defined as “when a one newton force acts on a body of area one meter square, then the pressure is one pascal”. Mathematically
Explanation:
Let’s take an example of a drawing pin. Hold the pin between a finger and the thumb, and the pointed part directed towards the thumb. By applying pressure we feel pain at the contact point at the thumb but not at the finger. This is because the pressure at the thumb is much higher than the pressure at the finger.
The reason is that the pressure is inversely proportional to the area. The pressure increase as the area decreases keeping the force constant. The area of the pointed part is very small as compared to the head of the drawing pin, so a pain is felt on the thumb.
“The normal force applied per unit area is called pressure”. It is denoted by “P”.
Mathematically:
The SI unit of pressure is pascal (Pa).
Pascal:
It can be defined as “when a one newton force acts on a body of area one meter square, then the pressure is one pascal”. Mathematically
Explanation:
Let’s take an example of a drawing pin. Hold the pin between a finger and the thumb, and the pointed part directed towards the thumb. By applying pressure we feel pain at the contact point at the thumb but not at the finger. This is because the pressure at the thumb is much higher than the pressure at the finger.
The reason is that the pressure is inversely proportional to the area. The pressure increase as the area decreases keeping the force constant. The area of the pointed part is very small as compared to the head of the drawing pin, so a pain is felt on the thumb.
Q.3) What is atmospheric pressure? How is it measured by using a mercury barometer? Also, describe how weather changes with atmospheric pressure?
Answer: Atmospheric Pressure:
“The pressure exerted by the gases in the atmosphere is known as atmospheric pressure”.
Answer: Atmospheric Pressure:
“The pressure exerted by the gases in the atmosphere is known as atmospheric pressure”.
Barometer: Atmospheric pressure is measured by using mercury barometer.
Construction:
A long tube opened at one end is filled with mercury and inverted in a dish of mercury. The mercury does not empty into the bowl. Instead, the atmospheric pressure pushes the mercury in the tube to some height ‘h’ above the bowl. In this way the force exerted on the bowl of mercury by the atmosphere is equal to the weight of the column of mercury in the tube.
A change in the height means a change in the atmospheric pressure.
Weather changes: When we keep a barometer at some height at sea-level, it shows some variation in atmospheric pressure from day to day.
The winds move from higher to lower pressure regions and the strength of the wind depends upon the pressure gradient. There will be strong winds if the pressure gradient is high and vice versa in this way weather changes with atmospheric pressure.
Construction:
A long tube opened at one end is filled with mercury and inverted in a dish of mercury. The mercury does not empty into the bowl. Instead, the atmospheric pressure pushes the mercury in the tube to some height ‘h’ above the bowl. In this way the force exerted on the bowl of mercury by the atmosphere is equal to the weight of the column of mercury in the tube.
A change in the height means a change in the atmospheric pressure.
Weather changes: When we keep a barometer at some height at sea-level, it shows some variation in atmospheric pressure from day to day.
The winds move from higher to lower pressure regions and the strength of the wind depends upon the pressure gradient. There will be strong winds if the pressure gradient is high and vice versa in this way weather changes with atmospheric pressure.
Q.4) State Pascal’s principle and explain with example?
Answer: Pascal’s principle
This principle states that ″whenever an external pressure is applied in a liquid, the pressure is transmitted equally to every point of the liquid in all directions.”
Or
“All liquids exert the same pressure in all directions.”
Answer: Pascal’s principle
This principle states that ″whenever an external pressure is applied in a liquid, the pressure is transmitted equally to every point of the liquid in all directions.”
Or
“All liquids exert the same pressure in all directions.”
Explanation:
Q.5) How pressure varies with depth in liquids? Explain.
Answer: The pressure in liquid increases with depth. Because the further down you go, the greater the weight of the liquid above. It can be observed in the figure below that the water spurts out fastest and furthest from the lowest hole. A simple set-up in the following figure shows how water pressure increases with depth.
As we know P = ρgh
Consider a container is filled with water and having three opening ‘P1‘, ‘P2‘ and ‘P3‘ as shown in figure
The water form opening ‘P1‘, shoots out with the least force because the pressure at ‘P1‘ is very small due to smaller depth ‘h1‘.
At opening ‘P2‘, the water shoots out with medium force because, the pressure at ‘P2‘ is greater due to greater depth ‘h2‘ as compared to ‘h1‘.
At opening ‘P3‘, the water shoots out with maximum force because, the pressure at ‘P3‘ is greatest due to maximum depth ‘h3‘
Q.6) What is meant by buoyant force or upthrust in fluids?
Answer: Buoyant force: The force exerted by liquids in opposite direction against the weight of the body is known as upward thrust.
There are so many systems which work on the principle of Pascal’s law. For example, hydraulic press, hydraulic brakes in vehicles and the hydraulic lifts etc. Here, we take a simple example of a hydraulic press to understand it. Consider two interconnected cylinders having different diameters. The chamber is filled with incompressible fluid, and their top ends fitted with pistons as shown in figure.
Answer: The pressure in liquid increases with depth. Because the further down you go, the greater the weight of the liquid above. It can be observed in the figure below that the water spurts out fastest and furthest from the lowest hole. A simple set-up in the following figure shows how water pressure increases with depth.
As we know P = ρgh
Consider a container is filled with water and having three opening ‘P1‘, ‘P2‘ and ‘P3‘ as shown in figure
The water form opening ‘P1‘, shoots out with the least force because the pressure at ‘P1‘ is very small due to smaller depth ‘h1‘.
At opening ‘P2‘, the water shoots out with medium force because, the pressure at ‘P2‘ is greater due to greater depth ‘h2‘ as compared to ‘h1‘.
At opening ‘P3‘, the water shoots out with maximum force because, the pressure at ‘P3‘ is greatest due to maximum depth ‘h3‘
Hence, it is proved that pressure varies directly with depth.
Answer: Buoyant force: The force exerted by liquids in opposite direction against the weight of the body is known as upward thrust.
Explanation:
When an object is immersed in a fluid, the pressure on the lower surface of the object is higher than the pressure on the upper surface. The difference in pressure leads to an upward net force acting on the object due to the fluid pressure called up-thrust or buoyant force and phenomenon is called buoyancy.
If you try to push a piece of cork underwater, you feel the buoyant force pushing the cork back up.
The buoyant force arise because the fluid pressure at the bottom of the cylinder is larger than at the top.
Net force Fnet of the fluid on the cork is the buoyant force Fb.
Fup > Fdown because the pressure is greater at bottom of the beaker, hence the fluid exerts a net upward force.
When an object is immersed in a fluid, the pressure on the lower surface of the object is higher than the pressure on the upper surface. The difference in pressure leads to an upward net force acting on the object due to the fluid pressure called up-thrust or buoyant force and phenomenon is called buoyancy.
If you try to push a piece of cork underwater, you feel the buoyant force pushing the cork back up.
The buoyant force arise because the fluid pressure at the bottom of the cylinder is larger than at the top.
Net force Fnet of the fluid on the cork is the buoyant force Fb.
Fup > Fdown because the pressure is greater at bottom of the beaker, hence the fluid exerts a net upward force.
Q.7) State and explain Archimedes principle .
Answer: Archimedes principle: “The buoyant force acting on an object fully or partially submerged in a fluid is equal to the weight of the fluid displaced by the object”.
Answer: Archimedes principle: “The buoyant force acting on an object fully or partially submerged in a fluid is equal to the weight of the fluid displaced by the object”.
Explanation:
According to Archimedes principle every object experiences a buoyant force. The buoyant force will decrease the weight of the object which termed as apparent lose of weight. Whether it floats or sinks depends on the object’s density relative to the fluid. When we push a wooden block underwater and you will feel the upward buoyant force as in figure.
By Archimedes principle, the buoyant force equals the weight of water displaced; since water is denser than wood, the buoyant force is greater than the wood’s weight, and that is why wood floats. Now when submerged a coin. It’s denser than water, so the coin’s weight is greater than the weight of the displaced water. Hence the coin’s weight is greater than the upward buoyant force, and it sinks.
Whether an object will float or sink depends on the net force acting on it. This net force can be calculated as follows:
Fnet = FB – W (object)
Now we can apply Archimedes principle, using ‘mo‘ to represent the mass of the submerges object and ‘mf‘ as mass of fluid ‘g’ is acceleration due to gravity.
Fnet = mfg – mog
Remember that ‘m = ρV’, so the expression can be rewritten as follows:
Fnet = ρfVfg – ρoVog or Fnet = (ρfVf – ρoVo)g
for submerged object equal volume is displaced therefore
Vo = VB = V
therefore mo = ρoV and mB = ρBV
putting these values in eq. 1, we get
According to Archimedes principle every object experiences a buoyant force. The buoyant force will decrease the weight of the object which termed as apparent lose of weight. Whether it floats or sinks depends on the object’s density relative to the fluid. When we push a wooden block underwater and you will feel the upward buoyant force as in figure.
By Archimedes principle, the buoyant force equals the weight of water displaced; since water is denser than wood, the buoyant force is greater than the wood’s weight, and that is why wood floats. Now when submerged a coin. It’s denser than water, so the coin’s weight is greater than the weight of the displaced water. Hence the coin’s weight is greater than the upward buoyant force, and it sinks.
Whether an object will float or sink depends on the net force acting on it. This net force can be calculated as follows:
Fnet = FB – W (object)
Now we can apply Archimedes principle, using ‘mo‘ to represent the mass of the submerges object and ‘mf‘ as mass of fluid ‘g’ is acceleration due to gravity.
Fnet = mfg – mog
Remember that ‘m = ρV’, so the expression can be rewritten as follows:
Fnet = ρfVfg – ρoVog or Fnet = (ρfVf – ρoVo)g
A simple relationship between the weight ‘W’ of submerged object of mass mo and density ρo can be found by considering their ratio as follows:
for submerged object equal volume is displaced therefore
Vo = VB = V
therefore mo = ρoV and mB = ρBV
putting these values in eq. 1, we get
Q.8) What is elasticity? Explain
Answer: Elasticity: “The property of Solid materials to return to their original shape and size after removal of deforming force is called elasticity”.
For example, when we stretch a rubber band, its size increases, but after the removal of the force, the rubber band gets their original shape.
Similarly, when a racket hits a tennis ball, the shape of the ball is distorted or deformed, but it regains its original shape when it bounces off the tennis racket.
But the materials are elastic up to a certain limit known as the elastic limit. Beyond this limit, a material deforms and do not attain its original position.
Answer: Elasticity: “The property of Solid materials to return to their original shape and size after removal of deforming force is called elasticity”.
For example, when we stretch a rubber band, its size increases, but after the removal of the force, the rubber band gets their original shape.
Similarly, when a racket hits a tennis ball, the shape of the ball is distorted or deformed, but it regains its original shape when it bounces off the tennis racket.
But the materials are elastic up to a certain limit known as the elastic limit. Beyond this limit, a material deforms and do not attain its original position.
Q.9) State and explain Hooke’s law.
Answer: Hook’s law: This law states that “within the elastic limit, the extension (or compression) is directly proportional to the restoring force”.
Answer: Hook’s law: This law states that “within the elastic limit, the extension (or compression) is directly proportional to the restoring force”.
Explanation
Consider that a spring is connected with a firm support at its one end. And a force ‘F’ is applied on the object the other end of the spring to produce an extension ‘x’ Then release it. A restoring force F restoring of spring act on the object to restore its original position. According to Hook’s law, we have
Fres ∝ -x
Fres = k x
Where ‘K’ is constant of proportionality and is known as spring constant or modulus of elasticity. Its unit is Nm-1. The value of ‘K’ depends upon the nature of the spring and system of units.
Consider that a spring is connected with a firm support at its one end. And a force ‘F’ is applied on the object the other end of the spring to produce an extension ‘x’ Then release it. A restoring force F restoring of spring act on the object to restore its original position. According to Hook’s law, we have
Fres ∝ -x
Fres = k x
Where ‘K’ is constant of proportionality and is known as spring constant or modulus of elasticity. Its unit is Nm-1. The value of ‘K’ depends upon the nature of the spring and system of units.
Q.10) Define and explain, Stress, strain and Young’s modulus
Answer: Stress: “The force applied per unit area of cross-section to produce deformation”.
Mathematically,
The SI unit of stress is Nm-2 orpascal.
Answer: Stress: “The force applied per unit area of cross-section to produce deformation”.
Mathematically,
The SI unit of stress is Nm-2 orpascal.
Strain: The deformation produced in a body due to stress is called strain.
Consider a wire has an initial length “L”. After the applied deforming force, the length of the wire change to an amount “ΔL”. The linear strain can be defined as the change in length per unit original length is called linear strain.
It is denoted by a Greek letter Epsilon “ε”
Mathematically
The strain has no unit because it is the ratio of two similar quantities.
Consider a wire has an initial length “L”. After the applied deforming force, the length of the wire change to an amount “ΔL”. The linear strain can be defined as the change in length per unit original length is called linear strain.
It is denoted by a Greek letter Epsilon “ε”
Mathematically
The strain has no unit because it is the ratio of two similar quantities.
Young’s modulus: The ratio of the tensile stress to the strain is called Young’s modulus or modulus of elasticity. It is represented by ‘Y’.
The SI unit of Young’s modulus is Nm-2.
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