9th Class Physics Unit 8 Magnetism Short Questions and Answers

1.What are temporary and permanent magnets?

See theory of Q No.6.

2.Define magnetic field of a magnet.

See theory of Q No.7.

3.What are magnetic line of force?

See theory of Q No. 7 (ii)

4.Name some uses of permanent magnets and electromagnets.

See Q No. 8 and 10.

5.What are magnetic domains?

The group of atoms in ferromagnetic material form a region of about 0.1 mm size that is highly magnetized. This region is called as a magnetic domain. Each domain behaves as a small magnet with its own north and south poles.

6.Which type of magnetic field is formed by a current-carrying long coil?

A current-carrying long coil forms a solenoidal magnetic field, which is similar to the magnetic field of a bar magnet. When an electric current flows through the coil, a magnetic field is generated, with lines of force emerging from the north pole and entering the south pole. The magnetic field is strongest at the center of the coil and weakens as you move away from it. The solenoidal magnetic field is nearly uniform and is commonly used in applications such as electromagnets, transformers, and inductors.

1.Is isolated magnetic pole possible?

No, it is not possible if we break a bar magnet into two equal pieces, can we get N-pole and S-pole separately? No. it is not possible. Each piece will have its two poles, i.e. N-pole and S-pole. Even if a magnet is divided into thousands pieces, each piece will be complete magnet with its N. and S-poles (Fig).

2.Describe the direction of internal and external magnetic field.

The direction of internal magnetic field is from magnetic field is from North Pole to South Pole. But in case of internal magnetic field the direction of magnetic field is from South Pole to North Pole.

3.Explain use electromagnetic in maglev train.

A wonderful use of electromagnets is seen in the Maglev trains. This maglev stands for a magnetically levitated train. A maglev uses forces that arise from induced magnetism to levitate or float a few centimeters above the guideway. This is why, it does not need wheels and faces no friction. In Japan, it is known as a bullet train that can run up to a speed of 400 km per hour.

As described above, magnetic levitative only lifts the train and does not move it forward. To push the train forward, propulsion electromagnets are installed along the guideway and train. By push and pull of these magnets the train moves forward.

4.Why high field electromagnet are made by cores of soft iron.

The magnetism induced in a ferromagnetic material can be surprisingly large in the presence of weak external field. In come cases, induced field is a thousand times stronger than the external field. That is why high field electromagnets are made by using cores of soft iron of some other ferromagnetic material.

5.State some uses of electromagnet.

There are some uses of electromagnet:
(i) Magnetic Relay
(ii) Circuit Breaker
(iii) Telephone Receiver
(iv) Electromagnetic Cranes

6.State right hand grip rule.

Right hand Grip rule is stated as below:
"Grip the solenoid with the right hand such that fingers are curled along the direction of current (positive to the negative terminal of the battery) in the solenoid, then the thumb points to the N-pole of the bar end."

1.Two bar magnets are stored in a wooden box. Label the poles of the magnets and identify P and Q objects.

Two bar magnets are stored in a wooden box with poles labelled as the North (N) of one magnet faces the South (S) of other (N−S,S−N). P is the magnet connector used to preserve magnetism and Q is a non-magnetism material like wood or plastic.

2.A steel bar has to be magnetised by placing it inside a solenoid such that end A of bar becomes N-pole and end B becomes S-pole. Draw circuit diagram of solenoid showing steel bar inside it.

A steel bar to be magnetised is placed inside a solenoid (long coil of wire) as shown in the figure.

When direct current is passed through the solenoid, the steel bar becomes a magnet such that end A of a bar becomes N-pole and B becomes S-pol.

3.Two bar magnets are lying as shown in figure. A compass is placed at the middle of the gap. Its needle settles in the north-south direction. Label N and S poles of the magnets. Justify your answer by drawing field lines.

Refer to diagrams showing field line patterns and pole configurations.

4.Electric current or motion of electron produce magnetic field. Is the reverse process true that is the magnetic field gives rise to electric current? If yes, give an example and describe it briefly.

Yes, the reverse process is true a changing magnetic field can give rise to an electric current. This phenomenon is known as electromagnetic induction and is governed by Faraday's law of induction.

Example In an electric generator, mechanical energy is converted into electrical energy using electromagnetic induction. When a coil of wire is rotated within a magnetic field, the magnetic field through the coil changes continuously. According to Faraday law, this change in magnetic field induced on electromotive force (EMF) in the coil, when drives an electric current.

5.Four similar solenoids are placed in a circle as shown in figure. The magnitude of current in all of them should be the same. Show by diagram, the direction of current in each solenoid such that when current in each solenoid is switched off, the net magnetic field at the centre O is directed towards that solenoid. Explain your answer.

For Solenoid 1(Top) Current should flow in a counterclockwise direction, so the magnetic field at the center O will point downward when viewed from the top.

For Solenoid 2 (Bottom) Current should flow in a counterclockwise direction, so the magnetic field at the center O will point upwards when viewed from the bottom.

For Solenoid 3 (Right) Current should flow in a clockwise direction, so the magnetic field at the center O will point left when viewed from the right.

For Solenoid 4 (Left) Current should flow in a clockwise direction, so the magnetic field at the center O will point right when viewed from the left.

This arrangement ensures that the magnetic field produces by each solenoid will contribute to pointing towards the solenoid that is switched off, maintaining symmetry and achieving the desired effect.

1.How can you identify whether an object is a magnet or a magnetic material?

See Q No. 3

2.Describe the strength of a magnetic field in terms of magnetic lines of force. Explain it by drawing a few diagrams for the fields as examples.

See Q No .7

3.What is a circuit breaker? Describe its working with the help of a diagram.

See Q No. 10.

4.A magnet attracts only a magnet. Explain the statement.

A magnet attracts certain materials, not just other magnets. These materials include ferromagnetic materials like iron, nickel, and cobalt, as well as paramagnetic materials like aluminum and oxygen. When a magnet is brought near these materials, it induces magnetization in them, causing them to be attracted to the magnet. However, non-magnetic materials like wood, plastic, and glass are not attracted to magnets, and diamagnetic materials like copper and silver are actually repelled by them.

5.Differentiate between paramagnetic, diamagnetic and ferromagnetic materials with ferene to the domain theory.

See Q No. 12

6.Why ferromagnetic materials are suitable for making magnets?

See Q No. 13

Unit 8: Magnetism — Short Questions

Short Answer Questions (Exercise)

SLO based Additional Short Questions

Magnetic Poles

Electromagnet

Constructed Response Questions

Comprehensive Questions