Magnets and magnetic substances
A fridge door shuts with a soft "click" and stays closed. A tiny magnet inside the rubber strip holds it on to the iron body. An iron nail also sticks to it. Magnets pull some things and ignore others.
A magnet (चुंबक) attracts some substances. Substances attracted towards a magnet are magnetic (चुंबकीय); those that are not attracted are non-magnetic (अचुंबकीय).
Rule 1: Magnetic substances — Iron, cobalt and nickel are magnetic. Small pins, small nails and iron filings are attracted. If an iron article is very big or heavy, the magnet gets pulled towards it.
- Easy : An iron nail is attracted to a magnet.
- Medium : A steel paper clip is attracted because steel is mostly iron; but stainless steel is usually not magnetic.
- Exam-type : A big iron gate does not move, so the magnet moves towards it.
In the figure : In the figure the magnet attracts only the iron pin (A) and the steel clip (C). The plastic comb (B) and the glass marble (D) are non-magnetic.
Rule 2: Non-magnetic substances — Glass, plastic and wood are not attracted.
- Easy : A plastic ruler is not attracted.
- Medium : A wooden pencil and a glass bangle are not attracted.
- Exam-type : Nickel is used for shiny parts of vehicle-light rings and door handles; it is magnetic.
Only iron, cobalt and nickel (and things made from them) are magnetic.
Thinking every shiny metal is magnetic. Copper and aluminium foil are shiny but are not magnetic.
Memory clue: Iron – Cobalt – Nickel = I-C-N.
Spot the difference
| Point | Magnetic | Non-magnetic |
|---|---|---|
| Attracted by magnet | Yes | No |
| Examples | Iron, cobalt, nickel | Glass, plastic, wood |
Practice questions
- 1What is a magnet?
- 2Name the three magnetic substances.
- 3Name two non-magnetic substances.
- 4Will a magnet attract a wooden ruler?
- 5Why does a magnet attract a steel clip?
- 6What happens when a magnet is brought near a very big iron gate?
- 7Out of an iron pin, a rubber band, a copper coin and an iron nail, which two stick to a magnet?
- 8Sneha says aluminium foil is shiny so a magnet will stick to it. Is she right?
Show answers (try them yourself first)
- 1An object that attracts magnetic substances.
- 2Iron, cobalt and nickel.
- 3Glass and plastic (or wood).
- 4No
- 5Steel contains iron, which is magnetic.
- 6The magnet gets pulled towards the gate.
- 7The pin and the nail.
- 8No. Only iron, cobalt and nickel are magnetic, not all shiny metals.
Uses of magnets
When you swipe an ATM card, the machine reads the thin dark strip on the back. That strip holds your bank account information with the help of magnetism. Magnets work quietly inside many things we use every day.
Machines that produce electricity using magnets are electric generators (विद्युत जनित्र). An MRI machine in a hospital uses a magnet to examine blood vessels, muscles and internal organs without injury.
Rule 1: Magnets in machines — Strong magnets are needed to make powerful electric pumps that draw water from wells. Electric generators, motors, speakers, headphones and refrigerators also use magnets.
- Easy : Refrigerator door: a magnet keeps it shut.
- Medium : Headphones and speakers: magnets are inside.
- Exam-type : Power plants use generators with magnets to produce electricity.
Rule 2: Magnetic strips and medicine — An ATM card has a thin magnetic strip with the account holder's information. Computers use magnetic strips to save information. MRI machines in large hospitals can work only by using a magnet.
- Easy : ATM card strip → account information.
- Medium : MRI → looks inside the body without injury.
- Exam-type : In waste management a magnet separates magnetic material (iron pieces) from garbage.
Magnets are used in generators, pumps, ATM cards, MRI, speakers and refrigerators.
Keeping an ATM card near a strong magnet. It can spoil the information on the strip.
Memory clue: ATM = Account in a Thin Magnetic strip; MRI = Magnet Reads Inside.
Spot the difference
| Use | How the magnet helps |
|---|---|
| Generator | Produces electricity |
| ATM card | Magnetic strip stores information |
| MRI | Examines organs without injury |
Practice questions
- 1What is an electric generator?
- 2What does the strip on an ATM card contain?
- 3What does an MRI machine examine?
- 4Name two household things that have magnets.
- 5Which pumps need strong magnets?
- 6How does a magnet help in waste management?
- 7Why is it better to keep an ATM card away from strong magnets?
- 8Why can an MRI machine work only with a magnet?
Show answers (try them yourself first)
- 1A machine that produces electricity using magnets.
- 2Information of the account holder.
- 3Blood vessels, muscles and internal organs.
- 4Refrigerator and speaker (or headphones).
- 5Powerful electric pumps that draw water from wells.
- 6It separates magnetic material from garbage.
- 7Its magnetic strip stores information, which may be damaged.
- 8It needs a magnet to examine the inside of the body.
Freely suspended magnet and poles
A toy compass in a school fair always shows the same direction, however you turn the box. Any magnet that is free to swing does the same, like a weathercock that settles with the wind.
A pole (ध्रुव) is the part of a magnet where the magnetic force is greatest. The end of a freely hung magnet pointing north is the north pole (उत्तर ध्रुव); the end pointing south is the south pole (दक्षिण ध्रुव).
In the figure : In the figure most of the iron filings stick near the two ends of the bar magnet, where its poles are.
Rule 1: Poles — A magnet has two poles. The north and south poles cannot be separated. The force is greatest at the poles, so most filings stick to the ends.
- Easy : Dip a bar magnet in iron filings: the ends hold most.
- Medium : The middle of a bar magnet holds very few filings.
- Exam-type : Two poles in every magnet: there is no single-pole magnet.
In the figure : In the figure a bar magnet hangs from a wooden stand and rests in the north-south direction: the north pole (N) points to the north and the south pole (S) to the south.
Rule 2: Freely suspended magnet — A bar magnet hung by a thread from a wooden stand (wood is non-magnetic) always settles in the north-south direction.
- Easy : The stand is made of wood so it does not disturb the magnet.
- Medium : The coloured end of a laboratory magnet marks a special end (the north pole).
- Exam-type : Rotate the magnet and leave it: it comes back to the same north-south position every time.
Hung freely, a magnet always settles north-south. Its north pole faces north.
Using an iron stand or hanging it near iron. The stand must be non-magnetic, like wood.
Memory clue: North-seeking end = North pole.
Spot the difference
| Point | North pole | South pole |
|---|---|---|
| Points towards | North | South |
| Letter | N | S |
| Can it be separated? | No | No |
Practice questions
- 1What is a pole of a magnet?
- 2How many poles does a magnet have?
- 3In which direction does a freely hung bar magnet settle?
- 4Which end of a hung magnet is the north pole?
- 5Why do most iron filings stick at the ends of a bar magnet?
- 6Why is a wooden stand used and not an iron one?
- 7A bar magnet is cut into two equal pieces. How many poles will there be in total, and why?
- 8Meena hangs a magnet and it settles east-west. What mistake could she have made?
Show answers (try them yourself first)
- 1The part of the magnet where the magnetic force is greatest.
- 2Two
- 3North-south
- 4The end pointing north.
- 5The poles are at the ends, where the force is greatest.
- 6Wood is non-magnetic; iron would attract the magnet.
- 7Each piece has its own N and S, so 2 × 2 = 4 poles; poles cannot be separated.
- 8A magnetic or iron object was nearby, or the thread was twisted.
Natural and artificial magnets
Long ago a shepherd's stick-cap stuck to a stone on the hill and people wondered why. Today we make magnets in factories, but the first magnets were found in nature, as stones.
Natural magnets (नैसर्गिक चुंबक) are weak magnets found in nature, like magnetite. Artificial magnets (कृत्रिम चुंबक) are made by humans.
Rule 1: Natural magnets — Nobody knows who discovered the magnet. Chinese scripts 2500 years ago describe a stone that attracts iron and settles in the north-south direction. About 3500 years ago, polished long stones were used to find directions. The iron ore magnetite near the earth's surface is a natural magnet; scientists think lightning reactions made it so.
- Easy : Magnetite is a natural magnet.
- Medium : Chinese records are 2500 years old; the direction stones are 3500 years old. 3500 − 2500 = 1000 years older.
- Exam-type : The shepherd boy's story: stones from Magnesia stuck to the iron cap of his stick.
Rule 2: Artificial magnets — Alnico magnets are strong, made from aluminium, nickel and cobalt. Ceramic magnets are made from a special soil used for cups and saucers and fine metal powder; they are low-cost and used for decorative discs and toys.
- Easy : Alnico = Al + Ni + Co, a strong magnet.
- Medium : Ceramic magnets are low-cost, so used in toys.
- Exam-type : A small decorative disc on a fridge is often a ceramic magnet.
Natural = found in nature, weak (magnetite). Artificial = man-made (alnico, ceramic).
Thinking all magnets are man-made. Magnetite is natural.
Memory clue: Alnico = AL + NI + CO (Aluminium, Nickel, Cobalt).
Spot the difference
| Type | Made from | Use or feature |
|---|---|---|
| Natural (magnetite) | Iron ore in nature | Weak |
| Alnico | Aluminium + nickel + cobalt | Strong |
| Ceramic | Special soil + metal powder | Low-cost; toys, discs |
Practice questions
- 1What is a natural magnet?
- 2What is magnetite?
- 3What is an artificial magnet?
- 4Name the metals in an alnico magnet.
- 5Why are ceramic magnets used in toys?
- 6How old are the Chinese descriptions of the direction-seeking stone?
- 7How much older than the Chinese description (2500 years) are the direction stones used about 3500 years ago?
- 8Anil says every magnet is made in a factory. Correct him.
Show answers (try them yourself first)
- 1A weak magnet found in nature, like magnetite.
- 2An iron ore that is a natural magnet.
- 3A magnet made by humans.
- 4Aluminium, nickel and cobalt.
- 5They are low-cost.
- 6About 2500 years.
- 73500 − 2500 = 1000 years.
- 8Natural magnets like magnetite are found in nature.
Attraction, repulsion and the magnetic compass
Two magnets in your hand: sometimes they leap together with a click, sometimes they push each other away as if shy. A sailor in the middle of the sea has no road, yet his small compass shows the way.
Repulsion (प्रतिकर्षण) is pushing away; attraction (आकर्षण) is pulling together. The region around a magnet where its force acts is the magnetic field (चुंबकीय क्षेत्र). A magnetic compass (होकायंत्र) is a magnetic needle free to rotate on a support.
In the figure : In the figure unlike poles (a north pole facing a south pole) attract each other, and like poles (north facing north) repel each other.
Rule 1: Attraction and repulsion — Like poles repel; unlike poles attract. The force acts in the magnetic field around the magnet.
- Easy : N–S: attract.
- Medium : N–N or S–S: repel.
- Exam-type : If two magnets push apart when brought close, turn one around: they will attract.
In the figure : In the figure the red end of the compass needle points to the north (N).
Attraction, repulsion and the magnetic compass
In the app you can move this figure with your finger.
Open in the appRule 2: Magnetic compass — A magnetic compass works on the principle that a suspended magnet always settles in the north-south direction. It has been used for thousands of years to find directions at sea and in deserts.
- Easy : Read the red end of the needle: it shows north.
- Medium : Once north is known, south is opposite; east is to the right of a person facing north.
- Exam-type : Keep a compass away from iron and magnets, or it will point wrongly.
Like poles repel, unlike poles attract. A compass needle settles north-south.
Thinking like poles attract. They repel.
Memory clue: Opposites attract, likes repel.
Spot the difference
| Poles | Result |
|---|---|
| N and S (unlike) | Attract |
| N and N (like) | Repel |
| S and S (like) | Repel |
Practice questions
- 1What happens between like poles?
- 2What happens between unlike poles?
- 3What is a magnetic field?
- 4What is a magnetic compass?
- 5Which direction does the red end of the compass needle show?
- 6On what principle does a compass work?
- 7Two magnets push each other away when their ends are brought together. What should you do to make them attract?
- 8Ravi keeps a compass beside an iron box and the needle points wrongly. Explain.
Show answers (try them yourself first)
- 1They repel each other.
- 2They attract each other.
- 3The region around a magnet where its force acts.
- 4A magnetic needle free to rotate on a support; it shows directions.
- 5North
- 6A suspended magnet always settles in the north-south direction.
- 7Turn one magnet around so that unlike poles face each other.
- 8Iron attracts the magnetic needle, so it does not settle north-south.
Quick revision
- Iron, cobalt and nickel are magnetic; glass, plastic and wood are non-magnetic.
- A freely suspended magnet settles north-south; like poles repel and unlike poles attract.
- Magnets are used in generators, ATM cards, MRI machines and the magnetic compass.