Work

• In physics work (W) is said to be done, when a force (F) acts on the body and point of application of the force is displaced (s) in the direction of force

Work done = force x displacement     W=Fs

Unit of work

• Unit of work is joule(J).
• kilo joule(1000 joule)
• Mega joule (10 lakh joule)

James Prescott Joule

• He is best known for his research in electricity and thermodynamics.
• He formulated a law for heating effect of electric current.
• He also verified experimentally the law of conservation of energy.

Energy

• The energy of the body is defined as its capacity to do work.

Unit of energy

• Unit of Energy is also joule. One joule of energy is required to do one joule of work.

Different forms of energy

• Mechanical energy, chemical energy, light energy, heat energy, electrical energy.

Mechanical Energy

• Mechanical energy is of two types Potential energy 2.Kinetic energy

Potential Energy

• The energy possessed by a body by virtue of its position or due to state of Strain, is called potential energy.

Eg. weight lifting.

• Example: Water stored in reservoir has large amount of potential energy due to which it can drive a water turbine when allowed to fall down.
• This is the principle of production of hydro electric energy.

Expression for potential energy of a body above the ground level

          E_p=mgh.

Kinetic Energy

• Energy possessed by an object due to its motion is called kinetic energy.
• Kinetic energy of an object increases with its speed. Kinetic energy of an object moving with a velocity is equal to the work.

Expression for kinetic energy

         E_k mv²

Law of Conservation of Energy

• Energy can neither be created nor destroyed, but it is transformed from one form to another. Alternatively, whenever energy gets transformed, the total energy remains unchanged.

Proof-Freely falling body

Rate of Doing work (or Power)

• Power is defined as the rate of doing work or work done per unit time.

Unit of power

• The unit of power is J/S known as watt, its symbol is W.

1 watt                    1W=1 J S^-1

• Commercial unit of energy is kilo watt hour.
• We pay electricity bill in terms of unit or kWh. It is a commercial unit of electric energy consumed by the user.

Watt hour=power in watt x time in hour

Energy Transformation

Water from dam    : Potential energy into Kinetic energy

Microphone          : Sound Energy into Electrical energy

TV camera            : Light energy into Electrical energy

Solar Cell              : Light energy into Electrical energy

Iron Box               : Electrical energy into Heat energy

Loud speaker                  : Electrical energy into Sound energy

Fan                       : Electrical energy into Mechanical energy

Light                     : Electrical energy into light energy 

Inferences

• The same amount of heat supplied to different masses of same material will not give the same rise in temperature.
• But we can see the product of the mass and the rise in temperature will remain the same for all.
• Therefore the product of mass and rise in temperature can be taken as the measure of the quantity of heat.

Types of Energy

Different types of energy

Mechanical energy

• Water stored in a dam, flowering river, moving bus, galloping horse, a freely falling stone, and water stored in a  tank  possess energy.
• Water falling from a dam rotates turbines of a generator and generates electricity.
• The energy possessed by a body by virtue of its position is called potential energy.
• The energy possessed by a body by virtue of its motion is called kinetic energy.
• Potential energy and kinetic energy are called mechanical energy.

Uses

• Mechanical energy can bring a moving body to rest or can make a resting body move.
• Wind mill converts wind energy (kinetic energy) into electrical energy.

Chemical energy

• Energy released during chemical reaction is called chemical energy.
• For examples, chemical energy is related due to the chemical reaction taking place when wood, charcoal, petrol etc. are burnt.
• The food we eat undergoes chemical reaction and releases energy to do work.

Uses

• Chemical energy is used for the growth of plants and animals
• A battery or a cell converts chemical energy into electrical energy.
• Chemical energy of a fuel is converted into heat energy and light energy.
• Hydro power station at Mettur and Bhavani.
• “Heat is a form of energy”- James Joule.
• The unit of energy (Joule) is named after him.

Electrical energy

• Do you know why a fan rotates or an electric bulb glows when we switch on?
• In an electric bulb, electrical energy is converted into light energy and in an electrical fan electrical energy is converted into mechanical energy.
• In thermal power station heat energy,
• In wind mill, the wind energy is converted into electrical energy.

Uses

• In industries, electrical energy is used to operate machines.
• Electrical energy is also used in telecommunication.

Heat energy

• The chemical energy stored in wood and cooking gas is converted into heat energy.
• Due to friction and chemical reaction heat energy is produced.
• Discuss with your friends and find out various other sources of heat energy.

Uses

• The heat energy obtained from coal is used for generating electrical energy.
• The heat energy obtained from petrol and diesel is used to run vehicles.

Solar energy

• The energy obtained from the sun is called solar energy.
• What are the types of energy obtained directly from the Sun?

Uses

• Solar energy is directly used in solar heater, solar cooker, street light etc,
• Solar cells are used in artificial satellites and calculators.
• Solar energy is used to operate solar vehicles.

Conversion of energy

• In thermal power stations coal is burnt to generate electrical energy.
• Here the chemical energy of the coal is first converted into heat energy and then into electrical energy.
• Loud speaker converts electrical energy into sound energy.
• When water stored at a height flows down, its potential energy is converted into kinetic energy.
• The water rotates the turbines of a generator and electrical energy is generate.
• When wood, charcoal, petrol, diesel and other fuel are burnt chemical energy is converted into heat energy.
• During photosynthesis plants convert light energy from Sun into chemical energy and store it.
• In electric bell and horns of automobiles electrical energy is converted into sound energy.
• In a torch, light, chemical energy of the cell is first converted into electrical energy and then into light energy.
• Energy can neither be created nor be destroyed, but can be converted from one form into another form.
• This is called law of conservation of energy.

MEASURING INSTRUMENTS

Concept of small Measurements

• Physics is based on the study of systematic measurement. It is necessary to measure things accurately.

Measuring Length

• In a metre scale, the smallest length that can be measured is 1 mm. This is called the least Count of a metre scale.
• With the help of a Vernier Scale along with a metre scale, it is possible to measure length correct to 0.1 cm.

Least count            

• The smallest measurement that can be measured using a device or instrument is called least count of that instrument.

Least Count of a Vernier

• Least Count (LC) of a vernier is equal to the difference between a main scale division (MSD) and a Vernier scale division (VSD)

LC=1MSD-1 VSD

Vernier Calipers (Slide Calipers)

• This instrument is based on the principle of Vernier.

Least count of a Vernier calipers

• C = 0.1 mm = 0.01cm

Error

• It the Value is greater than that of actual value, it is called positive error. If the value is less than that of actual value, it is called negative error.

Zero Error of a vernier calipers

• If the zero of the Vernier scale coincides with the zero of the Main scale there is no zero error.

Positive Error

• If the zero of the Vernier scale is to the right of the Main scale zero, the zero error is positive and the zero correction (ZC) is positive.
• For example if the n^th division of the Vernier scale coincides with any division of the Main scale the Zero Error=+(n x L.C)

Negative Error

• If the zero of the Vernier scale is to the left of the Main scale zero, the zero error in negative and the zero correction (ZC) is positive.
• For example, if the n^th division of the Vernier scale coincides with division of the Main scale the

          Zero Error=-(10-n) x L.C

• Digital Vernier calipers that are used nowdays give visual readings at once, that is they show the measurements as numerical display .

Measuring Mass and Weight

Mass

• Mass of a body is the measure of the quantity of matter contained in the body.
• It does not very from place to place. The SI unit of mass is kilogram. It is measured using different types balances, which are the following.

Common (beam) balance

• A beam balance compares the sample mass with a standard reference mass using a horizontal beam

Physical Balance

• It is used in laboratories, to measure mass of an object correct to a milligram

Weight

• Weight is a measure of gravitational force on a body. It varies from place to place. It is measured using spring balance.

Spring balance

• It measures weight by the distance a spring stretches under its load.

MASS

• Mass is the amount of matter present in a body (or) is a measure of how much an object has.

WEIGHT

• Weight is the force which a given mass feels due to the gravity at its place (or) is a measure of how strongly gravity pulls on that matter.

DIFFERENCE BETWEEN MASS AND WEIGHT

Medical scale

• It is used to measure the body weight of human beings, it has a spring which compresses in proportion to the weight.

Digital balance

• It works on strain gauge (length sensitive electrical resistance) scale principle.

Weigh bridge

• It is used to measure weight of very heavy objects such as lorries and trucks using principle of strain gauge.

Hydraulic scale

• It is used to measure very heavy loads lifted by cranes which makes use of hydraulic force, to measure weight.

Measuring Time

• Recently digital clocks, atomic clocks and quartz clocks allow the measurement of small times accurately.

Sun dial

• It is based on the principle of the shadow of an object being formed on the ground when the sun rises and the sun sets.

Water clock

• These clocks are based on containers which are slowly filled with water coming out at a steady time.

Sand clock

• These clocks word similar to water clocks. Sand is used instead of wear.

Mechanical clock

• Galileo’s discovery of the pendulum led to the invention of pendulum clock.

Quartz clock

• Quartz crystal watches offer better performance and accuracy, quartz crystals vibrate with high frequency.
• These vibrations are used to indicate time in a liquid crystal display (LCD) digitally.

Atomic clock

• The most accurate clocks used now a days are atomic clocks. It is based on the principle of periodic vibration taking place within the cesium atom.
• In India the time standard is provided by atomic clock kept at National Physical laboratory, New Delhi.

Local time and Standard time

• Each country selects a standard meridian to set a uniform time irrespective of distances.
• The Standard meridian of India is 82.55^o E to calculate standard time. This time is called Indian Standard Time (IST)
• The standard meridian of England is Greenwich Meridian is called Greenwich Mean Time (GMT)
• IST is 51/2 hour ahead of GMT.i.e. 12 noon in England will be 5.30 pm in India
• An imaginary line drawn between north and south poles of the globe is called meridian.
• The meridian passing through the Royal observatory in Greenwich, England is taken as prime meridian with the origin of 0^o.
• When it is 7.00am in New York city, it is 12.00 noon in London, UK and already 9.00 pm in Tokyo, Japan.

SCREW GAUAGE:

• Screw Gauge is an instrument to measure the dimensions of very small objects upto 0.001 cm.

PRINCIPLE OF THE SCREW GUAGE

• Screw Gauge works under the principle of the screw. When a screw is rotated in a nut, the distance moved by the tip of the screw is directly proportional to the number of rotations.

PITCH OF THE SCREW

• Pitch of the screw is

            Pitch=

LEAST COUNT OF SCREW GAUGE

• The distance moved by the tip of the screw for a rotation of one division on the head scale is called the least count of the screw gauge.

L.C=

POSITIVE ZERO ERROR

• If the zero of the head scale lies below the pitch scale axis, the zero error is positive.

Z.E=+(n x L.C),

Z.C=-(n x L.C)

NEGATIVE ZERO ERROR

• E=-(100-n) x L.C,

Then the zero correction

Z.C = +(100-n)x L.C

MEASUREING LONG DISTANCE

• For measuring long distance such as distance of the moon or a planet from the earth, special methods are adopted.

ASTRONOMICAL DISTANCE

• Astronomical distance is the mean distance of the centre of the sun from the centre of the earth.

1.Astronomical unit (AU)

=1.496 x 10¹¹m

LIGHT YEAR

• Light year is the distance travelled by light in one year in vacuum.
• Distance traveled by light in one year in vacuum=velocity of light x 1 year (in seconds)

=3 x 10⁸ x 365.25 x 24 x60x 60

=9.465 x 10¹⁵m

Therefore, 1 light year = 9.467 x 10¹⁵m

• Newton concluded that all object in the universe attract each other. In the universe attract each other. This force of attraction between objects is called the gravitational force.