20 Amazing Tricks of Magnetic Effects

MAGNETIC EFFECTS OF ELECTRIC CURRENT
PHYSICS / CLASS-X

20 Amazing Tricks of Magnetic Effects

INTRODUCTION

It was found that magnetism and electricity are related to each other. This means that electricity can be used
for the generation of electromagnetic effect and this effect is called electromagnetism. Similarly changing
magnetic field can produce electricity, this is called electromagnetic induction.

Magnetism has been a source of curiosity for ages. Magnets are commonly found in science laboratories, toys
and in the magnetic stickers that we stick to refrigerators and steel almirahs. The earth itself acts as a magnet.
Actually, magnets are all around us, since each electron, proton and neutron behaves as a tiny magnet.

Magnetism has many uses –– from the simple magnetic sticker to magnetic resonance imaging (MRI). MRI is
a diagnostic technique in which the magnetism of the protons inside the human body is used to form images
of tissues.

20 Amazing Tricks of Magnetic Effects

Knowledge Based Questions:

1. A charge whenever in motion has
(A) only magnetic field linked with it
(B) only electric field linked with it
(C) both electric and magnetic field linked with it
(D) only gravitational field linked with it.

2. Magnetic forces
(A) are always attractive (B) are always repulsive
(C) may be attractive or repulsive (D) none of these

3. Magnetic field is generated by
(A) stone (B) mud (C) magnet (D) iron piece

4. A magnetic needle comes to rest in
(A) geographic East-west direction (B) geographic North-south direction
(C) vertical direction (D) in North-east direction

5. The device used for producing electric current is called
(A) generator (B) galvanometer (C) ammeter (D) motor

6. In an electric motor, conversion takes place of
(A) Chemical energy into electrical energy(B) Electrical energy into mechanical energy
(C) Electrical energy into light (D) Electrical energy into chemical energy

7. A magnet can be demagnetised by
(A) Hammering the magnet (B) Putting it in the water
(C) Cooling it (D) Putting in contact with iron

8. Which one of the following is the magnetic substance
(A) Mercury (B) Iron (C) Gold (D) Silver

9. Generally permanent magnets are prepared from
(A) Gold (B) Silver (C) Iron (D) Steel

10. If iron filings are sprinkled around a bar magnet then they arrange in a fixed pattern which is
(A) magnetic field lines pattern (B) Electric field lines pattern
(C) Faraday’s electric field lines pattern. (D) None of these

20 Amazing Tricks of Magnetic Effects

MAGNET

A substance which attracts small pieces of iron, nickel, cobalt and steel and points in North-South direction
when freely suspended (or hanged freely) is known as a magnet.

Natural magnets are irregular in shape, moreover they are weak magnets. An iron bar can be made a
magnet by rubbing it with a natural magnet. Such a magnet is known as Man made or artificial magnet. Like
magnetic poles (i.e. North and North or South and South) repel each other while unlike magnetic poles
attract each other.

20 Amazing Tricks of Magnetic Effects

Magnetite is so called because it was found is magnesia in Asia Minor.

The Greek discovered the attractive property of the natural magnet, while the Chinese discovered the directive property of the natural magnet.

In 1600, Dr. William Gilbert, the English physicist concluded that the Earth behaves as a large permanent magnet.

Artificial magnets are of different shapes. A bar magnet (i.e. rectangular in shape) and U-shaped magnet are common example of artificial magnets.

20 Amazing Tricks of Magnetic Effects

In the beginning, it was thought that electricity and magnetism have no relation with each other. However, in 1819, Hans Christian Oersted, a Danish physicist, discovered a relationship between electricity and magnetism. He found that a wire carrying current causes a deflection in the needle of a magnetic compass placed near the wire.

Since needle of a magnetic compass is a tiny magnet, so it will be deflected from its equilibrium position if another magnet is brought close to it. As the magnetic compass is placed near the current carrying wire, so the current carrying wire behaves as a magnet. The effect of the electric current passing through a wire due to which the needle of magnetic compass deflects is known as magnetic effect of electric current.

Try yourself
1. What is a magnet?
2. Can the poles of a bar magnet be separated?

20 Amazing Tricks of Magnetic Effects

Important Properties of Magnets

 Property of attraction :

Magnets attract small pieces of materials like iron, nickel, and cobalt. The property of a magnet to attract small pieces of iron seems to be concentrated in small regions at the ends of the magnet. These regions are called magnetic poles. The pole which points towards geographic north is called North pole of the magnet. The pole which points towards geographic south is called
South pole of the magnet.

20 Amazing Tricks of Magnetic Effects

 Property of direction :

A freely suspended magnet always aligns itself in the North-South direction.

 Like-poles of magnets repel each other and unlike-poles attract each other, just as like-charges repel and unlike-charges attract. Since a magnet can attract small pieces of iron and also the opposite pole of another magnet, property of attraction is not a sure test to find whether a given piece is a magnet or not. Repulsion is a sure test to confirm whether a given piece is a magnet
or not.

20 Amazing Tricks of Magnetic Effects

 Property of induction :

A magnet can induce magnetism in substances like soft iron, cobalt, nickel etc.

 Breaking a magnet successively into smaller pieces would still produce tiny magnets each with a north pole and south pole. The above phenomena is observed till we reach molecular stage.

20 Amazing Tricks of Magnetic Effects

 Magnetic poles always exist in opposite pairs. Single magnetic poles never exist.

When a bar magnet is suspended freely from its centre by a thread, one end of the magnet points towards the north of the earth and the other end of the magnet points towards the south of the earth.

The end of the magnet pointing towards north of the earth is called north seeking pole or simply north pole of the magnet. On the other hand, the end of the magnet pointing towards sound of the earth is called south seeking pole or simply south pole of the magnet.

You must have seen a magnetic compass needle. The needle of a magnetic compass is, in fact, a small bar magnet which is free to move in a horizontal plane on a pivot. One end of the compass needle pointing towards North is known as North Pole. The other end of the compass needle pointing towards South is known as South Pole.

When a north pole of a bar magnet is brought near the north pole of a magnetic compass needle, then the needle of the magnetic compass is deflected away from the north pole of the bar magnet.

On the other hand, when a north pole of a bar magnet is brought near the south pole of a magnetic compass needle, then the needle of the magnetic compass is attracted towards the north pole of the bar magnet. Thus, we conclude :
Like magnetic poles repel each other while unlike magnetic poles attract each other. The force with which a magnetic pole of a magnet attracts or repels another magnetic pole of another magnet is called magnetic force. The space or region around a magnet within which magnetic force is exerted on other magnet is called the magnetic field of the magnet.

20 Amazing Tricks of Magnetic Effects

Definition of Magnetic Field :

The space or region around a magnet (or a current carrying wire) within which its influence can be felt (or magnetic force is experienced) by another magnet is called magnetic field. It is denoted by B.

 To locate the magnetic field of a bar magnet, we use iron filings or a magnetic compass. When a magnetic compass is far away from a magnet, it is not deflected. However, when a magnetic compass is close to the magnet, it is deflected. So the space or region around a magnet within which a magnetic compass is deflected is known as the magnetic field of the bar magnet.

20 Amazing Tricks of Magnetic Effects

Magnetic Lines of Force (or Magnetic Field Lines) :

A magnetic field is represented by a series of lines (or paths) around a magnet. These lines represent the paths of an imaginary independent north pole if it were allowed to move freely in the direction of the magnetic force.

Definition of magnetic field line :

The path (straight or curved) along which unit north pole moves in a magnetic field (if free to do so) is called magnetic line of force or magnetic field line. Magnetic lines of force or magnetic field lines are helpful to show the direction and strength (or intensity) of a magnetic field.

20 Amazing Tricks of Magnetic Effects

Magnetic compass

The direction of the magnetic field at any particular place is the direction in which the north pole of a magnetic compass needle points if placed at that point. The strength of the magnetic field is shown by how much close these lines are to each other.

If magnetic field lines are very close to each other in a particular region, then the strength of the magnetic field in that region is very large. On the other hand, if the magnetic field lines are far from each other in a particular region, then the strength of the magnetic field in that region is very small.