6th cbse physics referance

7/29/2019 6th Cbse Physics Referance

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Evolution of TransportBefore the invention of the wheel, the only means of transportation was walking. For transporting goods, people usedanimals like donkeys, horses, mules, elephants, oxen, sled dogs, and even bison. Boats were also used as a means

of transportation on water. The earliest boats were simple logs of wood with a hollow cavity.

The oldest wheel was discovered in Mesopotamia, and is believed to be over 5,500 years old. Fixed wheels for cartswere invented around 3500 BC, according to some historians. After the invention of the wheel, man started usinganimals to pull vehicles that moved on wheels, and thus, bullock carts and chariots came into existence. Till the 19thcentury, most forms of transport used only animals

Motion and Measurement of Distances

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Walking was the first the means of transportation. Boats were used to transport goods on water. Early boats weresimple logs of wood with a hollow cavity. The invention of the wheel revolutionised transport. Wheel design wasimproved over thousands of years.

Till the beginning of the 19th century, people depended on animals for transportation of goods. Animals were usedto pull vehicles that moved on wheels. Popular vehicles, like the bicycle, were invented in the late 18th century. Thefirst bicycles made did not have any brakes. It was up to the rider to control the speed or stop the bicycle with his feet.

An exciting development was the fitting of motors on to bicycles. The steam engine and the railroad, too, wereinvented in the 19th century. The invention of the steam engine introduced a new source of power for transportation.Rail tracks were made for steam engine-driven carriages and wagons to transport goods.

The Wright brothers invented the airplane, and that is when the era of flying began. Electric trains, monorails,supersonic aeroplanes and spacecraft are some of the contributions of the 20th century. One of the most excitingdevelopments in travel is the flying train. It’s referred to as the flying train because it doesn’t touch the rails as itmoves. Huge magnets keep the train suspended in air.

Before the metrics for measurement were developed, people used several different means to calculate distanceandlength. For instance, a carpenter would measure the length of wood using his palms, fingers or arm. Similarly, a

cloth merchant would measure the length of cloth against an outstretched arm. To standardise measurements andensure consistency, standards needed to be set.

Foot length or palm length were commonly used as non-standard units of measurement. Historians say that theEgyptians formulated the cubit. The cubit was the base measurement for the pyramids. The point from where your elbow bends to the tip of the middle finger of your outstretched hand is the cubit.

However, scientists all over the world felt the need for uniformity in the standards for the measurement of lengths anddistances. Today, they all use a standard of measurement called the International System of Units or SI units. The SIunit for length is the metre, and is denoted by the small letter ‘m.’ For measuring large distances, as per SIstandards, we use the kilometre, denoted by two small letters ‘km.’ One kilometre is equal to 1000 metre.

The bicycle was invented in the late 18th century bicycles. The first bicycles did not have brakes, though. It was up tothe rider to the control the speed of the bicycle! Later on, motors were fitted to bicycles, and thus, mopeds came intoexistence. Further research and development led to the invention of the motors car.

The steam engine and the rail road were invented in the 19th century. Apart from these, motorised boats and shipswere used as a means of water transport. Roads, rail road and water remained the major means of transport for avery long time. The Wright brothers invented the airplane and gave the world another means of transport – airways.In his effort to explore his universe, man even stepped into space and invented the spaceship to travel in space.



There are various means of transport, such as road, rail, water and airways. The mode of transport can be chosen,usually depending upon the distance to be travelled, but sometimes also upon how fast you want to get to your destination.

Measuring Length and DistanceVarious means of measurement, such as the palms, fingers, arm length and feet, were used to measure length anddistance before standardised systems were introduced. Standards needed to be set to ensure consistency and tostandardise measurements. Several systems were devised, but almost the entire world now follows the metricsystem.

The base measurement for the pyramids is the cubit, which was formulated by the Egyptians. A cubit was measuredon the arm, from the point where the elbow bends, to the tip of the middle finger. One cubit is equal to 18 inches.However, the inch was invented by the Romans.

In order to avoid confusion in measurements, the French created in 1970 the metric system, which is a standard for measurement. A further development to ensure uniformity measurement of lengths and distances, and other quantities, was a standard of measurement called the International System of Units or SI.

The SI unit of length is the metre, and is denoted by the small letter ‘m’. This is the bas ic unit of length.1 metre =100 centimetres1 centimetre=10 millimetres10 millimetres=1 centimetreLarge distances are measured in kilometres, and 1 km=1000 m.The length and type of an object determines the kind of measuring tool one can use.

Measuring Length and its Accuracy

Measuring Length and its AccuracyA ruler is used to measure the length of an object. It is also used to measure the length of a straight line.




A ruler is used to measure the length of an object. It is also used to measure the length of a straight line. A non-stretchable stringor thread is used to measure the length of a curved line.

Procedure to Measure the Length of an Object (or) a Staight Line

First place the ruler along the edge of the object that is to be measured, with the zero mark of the ruler placed at one end

of the object.

On the ruler, note the reading at the other end of the object.

This gives the measure of the length of the object.

The same procedure can be followed to measure the length of a straight line.

Procedure to Measure the Length of a Straight Line Using a Damaged Ruler

Place the broken or damaged ruler along the edge of the object that has to be measured in such that any visible mark

coincides with one end of the object.

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Now note the reading on the ruler at the other end of the object.

The difference between the two readings is the length of the object.Accuracy

Whatever method you use, always look at the ruler with the eyes directly in the line with the reading and not in an oblique way toobtain the readings accurately.

Procedure to Measure the Length of a Curved Line

Take a non-stretchable string or a thread and tie a knot at one of its ends.

Place the knotted end of the thread at one end of the curved line.

Holding the thread steadily with your fingers, and stretch it along the curved line until you reach the other end.

Now make a mark on the thread where it reaches the other end.

Finally, place the thread along a metre scale and measure the length between the knot and the marked point.

This gives the length of the curved line.

Measuring Length and its Accuracy

Measuring Length and its AccuracyLength is one of the fundamental quantities




Length is one of the fundamental quantities. To measure the length of any object, place a ruler along the edge of that object withthe zero mark of the ruler placed at one end of the object. Then, note the reading on the ruler at the other end of the object. Thisgives the measure of the object’s length. When noting the reading on a ruler, you should look at it with the eyes directly above

the reading, and not in an oblique way. Otherwise, you will not be able to note the readingaccurately. If the zero mark of theruler does not coincide with the first end of the object, then the difference between the readings at the two ends gives the lengthof the object.

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The circumference of a cap forms a curved line. To measure the length of a curved line, tie a knot on one end of a piece of thread. This becomes the starting point for measurement. Now, place this knotted end at the starting point of the curved line thatyou want to measure. Then stretch the thread along the curved line, keeping it in place with your fingers and thumb. Keep

stretching the thread along the curved line until you reach the end of the line. Use a pen to make a mark on the thread at th e pointwhere it reaches the other end of the curved line. Now, place this thread along a metre scale and measure the length between the

knot and the marked point. This gives you the length of the curved line, which is the edge or the circumference of the cap.




RestWhen a body remains in one position for a long time, it is said to be at rest. For example, the chairs of the diningtable are at rest unless and until they are moved, and the flower vase, table, and the blackboard in the class room areall at the position of rest.

MotionThe act, process or state of the change in place or positionof a body with respect to time and relative to the observer is said to be motion. For example the blades of a rotating fan, the hands of a working wall clock, a moving car, a spinning top andsatellites are all in motion.

Rest and m ot ion are relat ive terms

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A body seems to be at rest with respect to one object, but may appear to be in motion with respect to some other object.For example, a person on a railway platform is at rest with respect to another person on the same platform, but is inmotion with reference to a person looking at him from a train crossing that platform. Similarly, a passenger sitting inthe train will appear at rest to another passenger on the same train.

Types of MotionThe var ious types of mot ion are

Rect i l inear m ot ion

Rectilinear motion is the motion of an object that moves in a straight line.For example, a train moving on a track, a parade, coins tossed in the air are all in rectilinear motion.

Circular mot ion

Circular motion is the motion of an object that moves at a fixed distance from a fixed point. Here, all objects rotate incircular motion. So, circular motion is motion in which the body traverses a circular path. The hands of a clock, amerry-go-round, the blades of a fan, the wheel of a moving vehicle, satellites, a spinning top, are all good examplesof circular motion.

Periodic mot ion

Periodic motion is motion that repeats itself at regular intervals of time. Every body executing circular motion can besaid to be executing periodic motion. For example, the pendulum of a wall clock moves at regular intervals, the bellsin a church, a bouncing ball, a vibrating string and a swinging cradle are all in periodic motion.

Somet imes an object can display comb inat ions of dif ferent types of mot ion :

For example

A moving car which moves straight on the road displays rectilinear motion but at the same time the wheels of the car

which are moving in circles display circular motion. So a moving car displays both rectilinear and circular motion.

In a sewing machine, the needle is in periodic motion whereas the wheels of the sewing machine are in circular motion. So

a sewing machine displays circular and periodic motions.

Rest and MotionIf a body does not change its position with respect to time, then it is said to be at rest.




If a body does not change its position with respect to time, then it is said to be at rest. If a body changes its position with respectto time, then it is said to be inmotion. There are different types of motion. Rest andmotion are relative terms. If you consider a

passenger in a moving train, he is at rest with respect to his co-passengers, but is in motion with respect to an observer on the

ground.

There are many examples of bodies that are relatively at rest. Trees, buildings and mountains are some examples of bodies thatare relatively at rest with respect to each other. Some examples of bodies in motion are flying birds, moving trains, and the

rotating blades of a ceiling fan.

There are different types of motion. They are rectilinear motion, circular motion and periodic motion.

Rect i l inear m ot ion

Rectilinear motion is the motion of a body in a straight line. Examples of bodies in rectilinear motion are sprinters in a racealong a straight track, the march-past of soldiers in a parade, and a bullet fired from a gun.

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Circular mot ion

When a body moves along a circular path, it is said to be in circular motion. Examples of bodies in circular motion are therotating blades of a fan, children playing on a merry-go-round, and the hands of a clock.

Periodic mot ion

When the motion of a body repeats itself after a certain time period, it is called periodic motion. The motion of a pendulum in a pendulum clock, and the motion of needle in a sewing machine are some examples of periodic motion.



Types of Media

Types of MediaObjects that emit light on their own are called luminous objects




Luminous ob jec ts

Objects that emit light on their own are called luminous objects. The light emitted by luminous objects enables us to see thingsaround us. Examples of luminous objects are a tubelight, the sun, a lit candle, glowing bulb, a bonfire and a lit torch.

Non- luminou s objects

Objects that do not emit light on their own are callednon – luminous objects. The light emitted by luminous objects falls on non-luminous objects, and then bounces back to our eye, which enables us to see non-luminous objects. Examples of non-luminous

objects are the moon, a book, a pen, a wooden box, a cupboard and a chair.

Opaque objects

Objects through which we cannot see are called opaque objects. A medium that does not allow light to pass through it is calledan opaque medium. Examples of opaque medium are a pencil box, a wooden screen, a book, a towel, a ceramic plate and chart

paper.

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Transparent objects

If we are able to see anything clearly through an object, then such an object is said to be a transparent object. A medium thatallows all the light incident on it to pass through it is called a transparent medium. Examples of transparent objects are plain

glass, a reading glass, a plastic scale, windowpanes, a soap bubble and pure water.

Translucent media

Objects that allow only a part of the light incident on them to pass through it are called translucent media. Examples of translucent media are a shower stall, smoked glass, sun glasses and butter paper.

Light travels in a straight line, and its rays represent the path of light

ypes of Media

Types of MediaObjects that emit light on their own are called luminous objects




Objects like the sun that give out or emit light of their own are called luminous objects. Objects like the moon and planets that donot give out or emit light are called non-luminous objects. You can see objects when light from luminous objects incidents onthem and reflects towards your eyes. The material that light passes through is called a medium.

There are three types of media. They are transparent,translucent and opaque. Material that allows the entire light incident on itto pass through is called atransparent medium. Examples of transparent medium are clear glass and clear water.

Material that allows a part of the incident light to pass through it is called a translucent medium. Examples of translucent

medium are butter paper, tissue papers and ground glass.

Material that does not allow light to pass through it is called an opaque medium. Most objects in our surroundings, like buildingsand trees, are opaque objects.

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Shadows and Pin Hole Camera

Shadows and Pin Hole CameraAn opaque object blocking the path of light is called ashadow.




ShadowAn opaque object blocking the path of light is called ashadow. A shadow is a dark region, and is formed only when a lightsource, an opaque object and a screen are present. For example, during a lunar eclipse, we see a part of the earth’s shadow o n thesurface of the moon. This happens when the earth, the sun and the moon are in a straight line, with the earth between the sun and

the moon. Here, the sun acts as the light source, the earth as the opaque object, and the moon as the screen. Opaque objects formshadows because light is not able to bend around them.Shadows are seen more clearly on light screens. Whatever the colour of the object, its shadow is always black because it is notilluminated by light. The length and shape of a shadow depends on the object by which it is formed. In the olden days, shadows

caused by objects placed in the sun were used to measure time. Such a device is called a sun dial. The Jantar Mantar in Jaipur consists of a sundial or Samrat Yantra, which can be used to tell the time, as its shadow moves visibly at one millimetre per second, or roughly six centimetres every minute.

Pinhole CameraThe image formed by a pinhole camera is inverted and smaller in size when compared to the original object. These cameras work on the principle that light travels in a straight line. Pinhole cameras are cheap and simple to make. An eclipse can be viewedusing a pinhole camera.

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Making a Pinhole Camera

Take two rectangular boxes that fit into one another without leaving any gap.

Cut open one side of each box.

Make a small hole in the larger box at the centre of the closed end opposite the side that has been cut open.

Cut a square of side five centimetres in the smaller box in the closed end opposite the side that has been cut open. Cover

this square with tracing paper.

Finally, slide the smaller box into the larger box, ensuring that the pinhole and the tracing paper are in line with one

another, but at the opposite ends.

Slide the smaller box to adjust the focus so that you can capture the image of any object you want.

This is the basic structure of the pinhole camera. However, the developed form of a pinhole camera uses photosensitive filminstead of translucent paper to capture images. The film can be developed later to obtain photo prints. Nowadays, of course, weuse digital cameras that store images in a computer chip. However, the basic principle of capturing the image remains the same.

An area that is not or is only partially irradiated or illuminated because of the interception of radiation by an opaqueobject between the area and the source of radiation is called a shadow. Shadows take the form of the outline of theobject that intercepts the light in its path. Thus, the dark outline of the opaque object that you see is a shadow.

To form a shadow, we need a source of light, an opaque object in the path of light, and a screen on whicha shadow is formed.

The shape of the shadow of an object is dependent neither on the colour of the object nor on the colour of thescreen.

If the distance of the object from the source is decreased, then the size of the shadow increases, provided thedistance between the source and the screen is constant. Maintaining the distance of the screen from the source, if the object is moved away from the source, then the size of its shadow decreases.

If the distance between the object and the screen is constant, and if the light source is moved towards the object,then the size of its shadow increases. On the other hand, if the distance between the object and the screen isconstant, and if the light source is moved away from the object, then the size of its shadow decreases.

Another factor affecting the size of the shadow is the distance between the object and the screen. If the distancebetween the object and the source of light is maintained constant, and if the screen is moved away from the object,then the size of the object’s shadow decreases. On the other hand, if the screen moves towards the object, then thesize of its shadow increases.

The size and shape of the shadow of an object depends on the orientation of the object with respect to the beam of light. The shadow changes in size and shape when the object is placed in a different way in the path of light.



Mirrors and Reflection


The likeness of an object carried and formed by light in a mirror is called an image.




ImageThe likeness of an object carried and formed by light in a mirror is called an image. For example, your image is a reflection of your face in the mirror. An image can be seen in the mirror because the light reflected from an object falls on the mirror and it isreflected. So, light incident on any smooth shiny surface like a mirror bounces back into the same medium. This bouncing of l ight

by any smooth surface is called reflection of light.Mirrors change the direction of light incident on them. The image in a planemirror is the same size and colour as that of the object. Moreover, the distance between the image and the mirror, is the same asthe distance between the mirror and the object.

ShadowWhen an opaque object blocks the path of light, a shadow is formed. A shadow is a black dark outline. Its length changes with achange in the position of the source of light. Shadows can be seen only on a surface or a screen.

Two-Way Mirror A glass that acts as a mirror on one side and plain glass on the other is called a two-way mirror. A two-way mirror is used when

you want to observe people without letting them know that they are being watched, for example, by police or in psychologicalinstitutions.

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Pinhole CameraImages formed by a pinhole camera are entirely different from the images that are formed by a mirror. The image formed by a

pinhole camera is inverted and smaller in size when compared to the object. The image is also not clear. Moreover, the distance

between the object and the pinhole is not the same as the distance between the pinhole and the image.A periscope is an instrument used for observing objects from a hidden position. This instrument is mostly used in submarines,and works on the concept of reflection in plane mirrors. Using mirrors, it enables people in a submarine to view objects on the

surface of the water.


Mirrors and ReflectionThe likeness of an object carried and formed by light in a mirror is called an image.




Reflection is the phenomenon in which light incident on an object bounces back into the same medium throughwhich it was propagating while incident on the object, following some laws. The path along which light propagates iscalled a light ray. When a light ray is incident on an object, it is called the incident ray. The ray that bounces backby the object into the same medium called the reflected ray.

A smooth plane surface that reflects the entire light incident on it is called a plane mirror . Light incident on an objectis reflected by that object. That reflected light incidents on the mirror, and is reflected again. It is because of this

reflection that we see images. Animage is the likeness of an object carried and formed by light in a mirror. In other words, your image is a reflection of your face in the mirror. In ancient times, people mostly used pools of still water, or water collected in a vessel as mirrors. The first man-made mirrors were in the form of a polished stone made by usingobsidian, a naturally occurring volcanic glass.

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The similarity between a shadow and an image is that neither can exist without light. However, there are somedifferences between shadows and images. Shadows are black, whereas images are colourful. Shadows of objectsplaced in the sun change in length with the position of the sun through the day. Your shadow will be at its longest atdawn or early morning, and at dusk or early evening, whereas it will be at its shortest at noon. An image in a planemirror doesn’t change in size at all; it is always the same size as that of the object. An image in a mirror can be seenwithout a screen, whereas it is mandatory to have a screen to form a shadow.

Electric Cell and Torch Bulb

Electric Cell and Torch BulbAn electric cell provides electricity to various devices that are not directly fed by the supply of electricity.




An electric cell provides electricity to various devices that are not directly fed by the supply of electricity.

Electric Cell

An electric cell consists of two terminals. One is a positive terminal and the other one is a negative terminal. A chemical that

helps produce electricity to connected devices.

Bulb

A bulb consists two terminals. A filament is a spirally wound wire inside the bulb supported by two thick wires at its ends. An

electrical cell is connected to the terminals of a bulb so that electricity from the cell can pass through the bulb. This electricitymakes the filament in the blub glow and emit light.

Electric Cell and Torch Bulb

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Electric Cell and Torch BulbAn electric cell provides electricity to various devices that are not directly fed by the supply of electricity.




Elect r ic Cell and Torch Bulb

An electric cell is a device that supplies electrical energy to devices that function using electricity. Thus, an electric cell produceselectricity for a torch to glow. In fact, not only a torch, an electric cell provides electricity to a number of devices, such as toys,

alarm clocks, pocket radios and cameras.

An electric cell has a cap, just under which there is a plus sign. This is the positive terminal of the cell. At the other end of thecell, there is a flat metallic disc with a minus sign just above the disc. This metallic disc is the negative terminal of the cell. These

terminals of the cell can be used to connect it to various devices. Inside a cell, there is dark powdery stuff, which is the chemical.This chemical helps the cell to provide electricity to the device it is connected to.

When a cell is connected to a device, the strength of the chemical decreases. Finally, when the entire energy of the chemical isspent, the device connected to the cell stops functioning. A rechargeable cell or a storage battery can be recharged

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The bulb inside a torch has a filament. This filament is supported by two thick wires at its ends. When the positive and thenegative terminals of an electric cell are connected to the two terminals of a bulb, electricity passes through the filament and itstarts glowing. The terminals of the bulb are fixed in such a way that they do not touch each other. The bulbs that we use in our homes all look the same. In recent years, a different type of bulb has become popular - the compact fluorescent lamp, generally

referred to as a CFL. It is an energy-saving bulb, which has a longer life than an ordinary bulb.

Electric Circuit



Electric CircuitElectricity needs a path to pass from the positive terminal to the negative terminal of an electric cell.




Electricity needs a path to pass from the positive terminal to the negative terminal of an electric cell. A connection that providesa path outside an electric cell, for the electricity to pass from the positive terminal to the negative terminal of the cell, is calledan electrical circuit.

For example, a bulb glows only when the positive terminal and the negative terminal of an electric cell are connected to the twoterminals of the bulb.

If the wires from the bulb are connected to the same terminal (either positive or negative), then the bulbdoesn’t glow.

Sometimes, the bulb may not glow even though the connections are properly made.

This is because the flow of electricity is incomplete as the filament in the bulb is broken. A broken filament bulb is said to be fused.

A device that is used to stop the flow of electricity by breaking the circuit is called a switch. Switches have wide range of applications. Some common types are:

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Toggle switches, which are used in our houses.

Pushbutton switches, which are used in the starter of a water pump.

Joystick switches, which are used in the remote control unit of a toy car.

Properties of a Magnet

Properties of a MagnetSubstances that possess the property of attracting iron are called magnets.




Substances that possess the property of attracting iron are called magnets. The two ends of a magnet are called its poles. Allmagnets have two poles, and they are called dipoles. A magnet with a single pole doesn't exist. Since poles have high magnetic

power, they attract objects easily. The poles of a magnet are named as the north pole and the south pole. In order to identify the

poles, the north pole is usually painted in red colour. The other end of the magnet will, therefore, be the south pole. Inlaboratories, magnets are painted completely red in colour with a white dot to indicate the north pole. The other end will,therefore, be the south pole. A magnet can be cut into two pieces. Each piece will behave like an independent magnet, with anorth pole and a south pole.

Types of magnets

Bar magnets

In these magnets, the poles are located at the ends of the bar.

Cyl indr ical magnets

In these magnets, the poles are located at the two circular ends of the cylinder.

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Dumb -bel l shaped magnets

In such magnets, the poles are located at the two dumb-bell shaped ends.

Horseshoe magnets

In these magnets, the poles are located at the two free ends of the 'U' shape.

Compass

A compass is an instrument that is used to find the directions. It has a thin magnetic needle supported from a pivot so that it canrotate freely. The needle is placed over a dial with the directions marked. The entire assembly is placed inside an airtight box.

The north pole of the magnetic needle is painted red. The magnetic needle in the compass points in the north-south direction. Byaligning the dial properly, the directions can be found. In the ancient days, an old pointing device, called the south pointing fish,was used to know the directions. The head of the fish pointed towards the south.

Al ignment of a compass

Take a compass and make sure that the magnetic needle comes to rest. Rotate the box so that the red tip of the magnetic needle

coincides with the north mark of the dial. The compass is now aligned. Next, select any object around you. Then, with the help of the compass, identify the direction in which the object lies relative to you.

Law of magnets

Unlike poles attract each other and like poles repel each other.

Art i f ic ia l magnets

Magnets can be made artificially, too. A rectangular iron bar, an iron needle, a blade or an iron nail can be turned into a magnet by rubbing a bar magnet over it.

Precaut ions to protect magnets f rom losing th eir magnet ic propert ies

Never drop magnets from heights.

Never heat a magnet.

Do not hammer a magnet.Certain items such as CD's, DVD's, debit cards, credit cards or ATM cards, audio and video cassettes, and mobile phones containmagnetic material. Keep them away from magnets to prevent damage.

6th cbse physics referance

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