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Download 9th Class Physics Notes (Unit # 6) for Federal Board (FBISE) Islamabad

Download 9th Class Physics Notes (Unit # 6) for Federal Board (FBISE) Islamabad

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Download 9th Class Physics Notes (Unit # 6) for Federal Board (FBISE) Islamabad


Question: Define work.  What is its SI unit?
Work is done when a force acting on a body displaces it in the direction of a force. Work is a scalar quantity.  It depends on the force acting on a body, displacement of the body and the angle between them.
Work done =      Force  x  displacement
W             =      FS
Unit of work:
Sl unit of work is joule (J). It is defined as:
The amount of work is one joule when a force of one Newton displaces a body through one metre in the direction of force.

Question: Derive  the  relation   for  work  done  by  a  force  inclined  with  the displacement?
Let the  force  F is making an angle 0 with the surface on which the body is moved. Resolving F into its perpendicular components Fx and Fy as,
Fx     =      F cos 0
Fy      =      F sin 0
In case  when  force  and  displacement  are  not  parallel  then  only  the  X­component Fx parallel to the surface causes  the body  to move on the surface  and not the y-component Fy.

Question: Define energy, give two types of mechanical energy.
A body possesses energy if it is capable to do work.
Types of mechanical energy:
Mechanical energy possessed by a body is of two types:
i)            Kinetic  energy
ii)           Potential energy.

Question: List the different forms of energy with examples?
Energy exists in various forms. Some of the main forms of energy are given:
i)      Mechanical Energy               ii)     Heat Energy
iii)    Electrical Energy                  iv)     Sound Energy
v)     Light Energy                       vi)     Chemical Energy
vii)    Nuclear Energy

Question: Describe mechanical energy with examples.
·        The energy possessed by a body both due to its motion or position is called mechanical energy.
·        For example Water  running   down  a  stream,  wind, a  moving  car,  a  lifted  hammer,  a stretched   bow,  a  catapult  or  a  compressed  spring  etc. possesses   mechanical energy.

Question: Describe heat energy with examples?
Heat is a form of energy given out by hot bodies. Large amount of heat is obtained by burning fuel. Heat is also produced when motion is opposed by frictional forces. The foods we take provide us heat energy.
The sun is the main source of heat energy.

Question: Describe electrical energy with examples?
Electricity is one of the widely used form of energy. Electrical energy can be supplied easily to any desired place through wires.
We   get electrical energy from batteries and electric generators. These electric generators are run by hydro power, thermal or nuclear power.

Question: Describe sound energy with examples?
When you knock at the door, you produce sound. Sound is a form of energy.
It is produced when a body vibrates; such as vibrating diaphragm of a drum, vibrating strings of a sitar and vibrating air column of wind instruments such as flute pipe etc.

Question: Describe light energy with examples?
Light is an important form of energy. Name some sources of light that you come across. Plants produce food in the presence of light. We also need light to see things.
We get light from candles, electric bulbs, fluorescent tubes and also by burning fuel. However most of the light comes from the sun.

Question: Describe chemical energy with examples?
  • Chemical energy is present in food, fuels and in other substances. We get other forms of energy from these substances during chemical reactions.
  • The burning of wood, coal or natural gas in air is a chemical reaction which releases energy as heat and light.
  • Electric energy is obtained from electric cells and batteries as a result of chemical reaction between various substances present in them.
  • Animals get heat and muscular energy from the food they eat.

Question: Describe nuclear energy with examples?
Nuclear energy is  he energy released in the form of nuclear radiations in addition  to  heat  and  light  during  nuclear  reactions  such  as  fission  and  fusion reactions.
Heat energy released in nuclear reactors is converted into electrical energy.
The energy coming from the Sun for the last billions of years is the result of nuclear reactions taking place on the Sun.

Question: What is Pole vaulter?
A pole vaulter uses a flexible vaulting pole made of special material. It is capable to store all the vaulter's kinetic energy while bending to the form of potential energy. The vaulter runs as fast as possible to gain speed. The  kinetic  energy gained  by  the  vaulter  due  to  speed  helps  him/her  to  rise  up  as  the  vaulter straightens. Thus he attains height as the pole returns the potential energy stored by the vaulter in the pole.

Question: List the major sources  of energy?
i)      Fossil fuels                         ii)     Nuclear fuels
iii)    Energy from biomass           iv)     Energy from water
v)     Energy from the sun            vi)     Solar house heating
vii)    Solar cells                          viii)   Wind energy
ix)     Geothermal energy

Question: Differentiate energy resources as renewable and non-renewable resources of energy with examples of each?
Renewable sources of energy are those which can be reused. They do not get extinguished.  They are environmentally friendly. They do not cause pollution. Examples:
Solar energy, wind energy and tidal energy.

Non-renewable sources of energy are those which cannot be reused. They get extinguished. They cause pollution and are environmentally harmful.
Plastic, wood, petroleum, oil, etc.

Question: List non-renewable sources of energy?
i.      Fossil fuels                 ii.     Nuclear fuels

Question: Describe the harmful waste  products released by fossil fuels?
List the Environmental issues associated with fossil fuels?
Fossil fuels release harmful waste products. These wastes include carbon mono-oxide and other harmful gases, wh1ch pollute the environment.  This causes serious health problems such as headache, tension, nausea, allergic reactions, irritation of eyes, nose and throat. Long exposure of these harmful gases may cause asthma, lungs cancer, heart diseases and even damage to  brain, nerves and other organs of our body.

Describe the processes by which energy is converted from one form to another with reference to nuclear fuels? OR List the Environmental issues associated with nuclear fuels?
·        In nuclear power plants, we get energy as a result of fission reaction. During fission reaction, heavy atoms, such as Uranium atoms, split up into smaller parts releasing a large amount of energy.
·        Nuclear power plants give out a lot of nuclear radiations and vast amount of heat. A part of this heat is used to run power plants while lot of heat goes waste into the environment.

Question: List non-renewable sources of energy?
i.      Energy from water       ii      Energy from the sun
iii.     Solar house heating     iv.     Solar cells
v.      Wind energy               vi.     Geothermal energy
vii.    Energy from biomass

Sunlight and water power are the renewable sources of energy. They will not run out like coal, oil and gas.

Question: How energy is obtained from water?
Energy from water power is very cheap. Dams are being constructed at suitable locations in different parts of the world. Dams serve many purposes. They help to control floods by storing water.  The  water  stored  in  dams  is  used  for irrigation  and  also  to  generate  electrical  energy  without  creating  much environmental problems.

Question: How energy is obtained from sun?
Solar energy is the energy coming from the Sun and is used directly and indirectly. Sunlight does not pollute the environment in any way. The sunrays are the ultimate source of life on the Earth. We are dependent on the Sun for all our food and fuels. If we find a suitable method to use a fraction of the solar energy reaching the Earth, then it would be enough to fulfill our energy requirement.

Question: Explain the functioning of solar house heating system?
Complete solar house heating systems are successfully used in areas with a minimum amount of sunshine in winter. A heating system consists of:
i.      A collector
ii.     A storage device
iii.     A distribution system

Working of solar heating system:
A solar collector made of glass panels over blank metal plates. The plates absorb the Sun's energy which heats a liquid flowing in the pipes at the back of the collector. The hot water can be used for cooking, washing and heating the buildings.
Uses of solar energy:
Solar energy is used in solar cookers, solar distillation plants, solar power plant, etc.

Question: State mass energy equation E = mc2
Einstein predicted the inter-conversion of matter and energy. According to him, a loss in the mass of a body provides a lot of energy. This happens in nuclear reactions. The relation between mass m and energy E is given by Einstein's mass-energy equation.
E      =      mc2
Here c is the speed of light (3 x 108 ms-1. The above equation shows that tremendous amount of energy can be obtained from small quantity of matter.

Question: What is meant by the efficiency of a system? OR How  can you find the efficiency of a system?
The ratio of the useful work done by a device or machine to the total energy taken up by it is called its efficiency.
                                Required form of output
Efficiency           =      --------------------------
                                Total input energy

                                Required form of output
%age Efficiency  =      -------------------------- x 100
                                Total input energy

Ideal system/Ideal machine:
An ideal system is that which gives an output equal to the total energy used by it. In other words, its efficiency is 100%.
People have tried to design a working system that would be 100% efficient. But practically such a system does not exist.

Question: When does a force do work? Explain.
  • Work  is  said  to be  done  when  a force  acts  on a body  and  moves  it in the direction of the force.
  • Greater is the force acting on a body and longer is the distance moved by it, larger would be the work done.
  • Mathematically, Work is a product of force F and displacement S in the direction of force.

Question: Why do we need energy?
The energy is an important and fundamental concept in science. It links almost all the natural phenomena. When we say that a body has energy, we mean that it has the ability to do work. Water running down the stream has the ability to do work, so it possesses energy. The energy of running water be used to run water mills or water turbines.

Question: Which form  of energy is most preferred and why?
Solar energy is the energy coming from the Sun and is used directly and indirectly. Sunlight does not pollute the environment in any way. The sunrays are the ultimate source of life on the Earth. We are dependent on the Sun for all our food and fuels. If we find a suitable method to use a fraction of the solar energy reaching the Earth, then it would be enough to fulfil our energy requirement.

Question: How is energy converted from one form to another?  Explain.
Energy cannot be created nor destroyed, but it can be converted from one form to another.
  • Rub your hands together quickly. You will feel them warm. You have used your muscular energy in rubbing hands as a result heat is produced. In the process of rubbing hands, mechanical energy is converted into heat energy.
  • Processes in nature are the results of energy changes. For example, some of the heat energy from the Sun is taken up by water in the oceans. This increases the thermal energy.

During the inter-conversion of energy from one form to other forms, the total energy at any time remains constant.

Question: Name   the   five devices that convert    electrical    energy into mechanical energy.
  • Electric motor converts electrical energy to mechanical energy.
  • Drill machine
  • Electric fan
  • Electric spinner
  • Electric grinder

Question: Name  a  device that  converts mechanical energy into  electrical energy.
Electric generator converts mechanical energy into electrical energy.

Question: What is meant by the term power?
Power is defined as the rate of doing work.

Power        =      P      =      Work done / Time Taken
                        P      =      w/t
Since work is a scalar quantity, therefore, power is also a scalar quantity.

Question: Define watt.
Sl unit of power is watt (W). It is defined as:
The power of a body is one watt if it does work at the rate of 1 joule per second.


Question: Define K.E. and derive its relation.
The energy possessed by a body due to its motion is called kinetic energy.
Derivation of K.E:
Consider a body of mass of body moving with velocity v. The  body  stops after moving through some  distance S due  to  some  opposing  force  such  as  force of friction acting on it. The body possesses kinetic energy and is capable to do work against opposing force F until all of its kinetic energy is used up.
K.E. of the body          =              Work done by it due to motion
K.E                            =              FS
Vi                             =              v
Vf                             =              0
F                               =              ma
a                              =              - F/m
Since motion is opposed, hence, a is negative. Using 3rd equation of motion:
2aS                           =              Vf2 - Vi2
2 (- F/m) S                 =              (0)2 – (v)2
-2FS/m                      =              -V2
FS                             =              ½ mv2

Question: Define potential energy and derive its relation.
The energy possessed by a body due to its position is known as its potential energy.
Derivation of P.E:
Let a body of mass m be raised up  through height h from the ground. The body will acquire potential energy equal to the work done in lifting it to height h.
Thus Potential energy  P.E   =      F x h
=      w x h
(Here weight of the body = w = mg)
P.E.   =      wh    =      mgh
Thus, the potential energy possessed by the body with respect to the ground is mgh and is equal to the work done in lifting it to height h.

Question: Why fossils fuels are called non-renewable form of energy?
  • Fossil fuels are known as nonrenewable resources because it took millions of years for them to attain the present form.
  • We use fossil fuels such as coal, oil and gas to heat our houses and run industry and transport.
  • They are usually hydrocarbons (compounds of carbon and hydrogen).
  • When they are burnt, they combine with oxygen from the air.
  • The carbon becomes carbon dioxide; hydrogen becomes hydrogen oxide called water; while energy is released as heat.
  • In case of coal:
Carbon  + Oxygen  ---------> carbon dioxide  + heat  energy
Hydrocarbon  + Oxygen -------> carbon dioxide  + water + heat energy
Describe   the   process   of   electricity generated by geothermal energy?
·        In some parts of the world, the Earth provides us hot water from geysers and hot springs.
·        There is hot molten part, deep in the Earth called magma.
·        Water reaching close to the magma changes to steam due to the high temperature of magma.
·        This energy is called geothermal energy.
·        Geothermal well can be built by drilling deep near hot-rocks at places, where magma is not very deep.
·        Water is then pushed down into the well.
·        The rocks quickly heat the water and change it into steam.
·        It expands and moves up to the surface.
·        The steam can be piped directly into houses and offices for heating purposes or it can be used to generate electricity.

Question: Describe the process of electricity generated by biomass?
·        Biomass is plant or animal wastes that can be burnt as fuel.
·        Other forms of biomass are garbage, farm wastes, sugarcane and other plants.
·        These wastes are used to run power plants. Many industries that use forest products get half of their electricity by burning bark and other wood wastes.
·        Biomass can serve as another energy source, but problems are there in its use.
·        When animal dung, dead plants and dead animals decompose, they give off a mixture of methane and carbon dioxide.
·        Electricity can be generated by burning methane.

Question: Describe the process of electricity generated by solar cells?
·        Solar energy can also be converted directly into electricity by solar cells.
·        A solar cell also called photo cell is made from silicon wafer.
·        When sunlight falls on a solar cell, it converts the light directly into electrical energy.
·        Solar cells are used in calculators, watches and toys. Large numbers of solar cells are wired together to form solar panels.
·        Solar panels can provide power to telephone booths, light houses and scientific research centers.
·        Solar panels are also used to power satellites.

Question: Describe the process of electricity generated by wind energy?
·        Wind has been used as a source of energy for centuries.
·        It has powered sailing ships across the oceans.
·        It has been used by windmills to grind grain and. pump water.
·        More recently, wind power is used to turn wind turbines.
·        When many wind machines are grouped together on wind farms, they can generate enough power to operate a power plant.




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Download Class Notes: Download 9th Class Physics Notes (Unit # 6) for Federal Board (FBISE) Islamabad
Download 9th Class Physics Notes (Unit # 6) for Federal Board (FBISE) Islamabad
Download 9th Class Physics Notes (Unit # 6) for Federal Board (FBISE) Islamabad
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