# FBISE 9th Class Physics Chapter 7 Properties Of Matter Short Questions Answers

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Class/Subject: 9th Class Physics

Chapter Name: Properties Of Matter

Board: Federal  Board

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## FBISE 9th Class Physics Chapter 7 Properties Of Matter Short Questions Answers

What is Plasma?

The kinetic energy of gas molecules goes on increasing if a gas is heated continuously. This causes the gas molecules to move faster and faster. The collisions between atoms and molecules of the gas become so strong that they tear off the atoms. Atom loses their electrons and becomes and positive ions. This ionic state of matter is called plasma.

What do you know about density?

The density of a substance is defined as its mass per unit volume.
Density = mass of a substance/volume of that substance

Define Pressure and write down its unit.

The force acting normally per unit area on the surface of a body is called pressure. Thus, P = Force/Area. Its unit is Nm-2.

What is Kinetic molecular theory?

Most of the properties of solids, liquids, and gas can be explained based on the intermolecular forces. The kinetic molecular model has some important features.

Write down the postulates of kinetic molecular theory?

i. The matter is made up of particles called molecules.
ii. The molecules remain in continuous motion. The motion of molecules could be linear, vibration, or rotational.
iii. The molecules attract each other.

Define pressure in liquids.

Liquid exerts pressure. The pressure of a liquid acts in all directions. If we take a pressure sensor (a device that measures pressure) inside a liquid, then the pressure of the liquid varies with the depth of the sensor.

State Pascal’s Law.

Pressure applied at any point of a liquid enclosed in a container is transmitted without the loss to all other parts of the liquid.
An external force applied on the surface of liquid increases the liquid pressure at the surface of the liquid. This increase in liquid pressure is transmitted equally in all directions and to the walls of the container in which it is filled.

State Archimedes Principle.

When an object is totally or partially immersed in a liquid, an upthrust act on it equal to the weight of the liquid it displaces.

Define the principle of floating?

A floating object displaces a fluid having weight equal to the weight of the object.

What is a barometer?

The instruments that measure atmospheric pressure are called barometers. One of the simple barometers is a mercury barometer. It consists of a glass tube 1 m long closed at one end.

What is atmospheric pressure?

The earth is surrounded by a cover of air is called the atmosphere. It extends to a few hundred kilometers above sea level. Just as certain sea creatures live at the bottom of the ocean, we live at the bottom of a huge ocean of air. Air is a mixture of gases. The density of air in the atmosphere is not uniform. It decreases continuously as we go up.

Explain the braking system of the vehicles.

The brakes of cars, buses, etc. work on the principle of Pascal’s law. In such a type of brake, when the brake pedal is pushed, it exerts pressure on the master cylinder, which increases the liquid pressure in the cylinder. The liquid pressure is transmitted equally through the liquid in the metal pipes. Due to increase pressure of the liquid pressure, the pistons in the cylinder mover outwards pressing the brakes pad with brake drums. The force of friction between friction the brake pads and the brake drum stops the wheels.

What is Elasticity?

The property of a body to restore its original size and shapes as the deforming force ceases to act is called elasticity.

What is Deforming force?

The applied force that changes the shape, length, or volume of a substance is called the deforming force.

What is Stress?

The force that acts on a unit area at the surface of a body and thus changes its shape or size is called stress.

What is a strain?

A comparison of change caused by the stress with the original length, volume, or shape is called the strain.

What is Hooke’s Law?

The strain produces in a body by the stress applied to it is directly proportional to the stress within the elastic limit of the body.

Define Young’s Modulus.

The rotation of stress and strain is a constant within the elastic limit, this constant is called the Young’s Modulus.

What is the elastic limit?

When stress is increased, the strain also goes on increasing until there comes a limit. When stress is removed, the object does not come back to its initial state. This limit of stress is called the elastic limit.

What are the elastic materials? Give some examples.

An object is said to be elastic if it restores its original size and shape after the external force ceases to act. For example rubber, plastic, nylon, iron, etc.

Prove that the SI unit of Young’s modulus in Pascal or Nm-2.

Pressure is calculated mathematically as:
P = F/A
P = N/m2 = Nm-2
Thus, the SI unit of pressure is Nm-2 and it is also named Pascal (pa).

Under what condition the object floats in water?

If the buoyant force ‘F’ is greater than the ‘w’ of the immersed object, the resultant force (F – w) will act in the upward direction and will push the object in an upward direction. In this situation, some parts of the object will be raised above the water so that the buoyant force ‘F’ becomes equal to the weight. So, equilibrium is established and the object floats.

Write any three applications of Pascal’s law in our daily life.

i. raw cotton and clothes are pressed to form their bundles for their easy transportation.
ii. For the service of heavy vehicles, these are lifted by the use of the hydraulic press.
iii. The brakes of certain vehicles work on the principle of a hydraulic press.

Under what condition the object sinks in water?

If the weight ‘w’ of the immersed object is greater than the buoyant force ‘F’ of the liquid, the resultant force (w – F) will act in the downward direction and the object will sink.

Define the term Pressure.

The force acting normally per unit area on the surface of a body is called pressure. P = F/A

It is easy to remove air from a balloon but it is very difficult to remove air from a glass bottle why?

This is because the air inside the balloon is a fair high pressure than the atmospheric pressure air outside the balloon. On the other hand air pressure inside the glass bottle is already equal to the atmospheric pressure so it is difficult to remove air from a glass bottle.

Why water is not suitable to be used as the barometer?

Mercury is 13.6 times denser than water. Atmospheric pressure can hold a vertical column of water about 13.6 times the height of the mercury column at a place. Thus, at sea level, the vertical height of the water column would be 0.76 m x 13.6 = 10.34 m. Thus, a glass tube more than 10 m long is required to make a water barometer.

What makes a sucker pressed on a smooth wall to it?

The sucker is dish-shaped, when pressed against a smooth surface the air is forced beneath the sucker. The rubber makes an airtight seal and the air pressure outside is greater than the air pressure beneath the sucker, thus forcing the rubber sucker to ‘stick’.

What is upthrust?

Upthrust is a force that pushes an object up and makes it seem to lose weight in a fluid. (Remember, a fluid means a liquid or a gas).

Explain how a submarine moves up the water surface and down into the water.

A submarine can travel over as well as underwater. It also works on the principle of floating. It floats over water when the weight of water equal to its volume is greater than its weight. Under this condition, it is similar to a ship and remains partially above water level. It has a system of tanks that can be filled with and emptied from seawater. When these tanks are filled with seawater, the weight of the submarine increases. As soon as its weight becomes greater than the upthrust, it dives into the water and remains underwater. To come upon the surface, the tanks are emptied from seawater.

Prove that liquid pressure does not depend upon the mass of the liquids.

Liquid pressure is given by the formula:
P = ρgh
The above equation is independent of the mass of the liquid. So, liquid pressure does not depend upon the mass of the body.

What is Hydrometer?

A hydrometer is a glass tube with a scale marked on its stem and heavyweight in the bottom. It is partially immersed in a fluid, the density of which is to be measured. One type of hydrometer is used to measure the concentration of acid in a battery. It is called an acid meter.

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