Exercise – Magnetism
Objective Questions
1. Iron, cobalt and nickel are a. Magnets b. Magnetic substances c. Non-magnetic substances d. None of these
Answer: Magnetic substances
2. Three rods X, Y and Z are given. X is a magnet, Y is a magnetic substance and Z is non-magnetic. Which rods can be attracted by a magnet? a. Only X b. Both X and Y c. Only Y d. None of these
Answer: Both X and Y
3. A freely suspended bar magnet always points in the a. North-West direction b. South-East direction c. North-South direction d. East-West direction
Answer: North–South direction
4. A soft iron bar placed across the poles of a magnet to prevent self-demagnetisation is called a. Magnetic keeper b. Magnetic compass c. Magnetic pole d. None of these
Answer: Magnetic keeper
5. Objects X and Z are attracted by a magnet while Y is not. The materials of X, Y and Z are a. Iron, brass and copper b. Aluminium, copper and cobalt c. Iron, copper and nickel d. Nickel, brass and copper
Answer: Iron, copper and nickel
Fill in the blanks
1. __________ is the sure test of magnetism.
Answer: Repulsion
2. __________ is an alloy of aluminium, nickel and cobalt.
Answer: Alnico
3. The two ends of a magnet are called __________.
Answer: Magnetic poles
4. The __________ property of a magnet helps in finding directions.
Answer: Directive
5. Magnetic poles always exist in __________.
Answer: Pairs
True or False
1. A magnet and magnetic material always attract each other.
Answer: True
2. Strength of natural magnets is fixed.
Answer: True
3. Magnetic field lines intersect at the poles.
Answer: False
4. A freely suspended magnet aligns in the east–west direction.
Answer: False
5. Hammering a magnet increases its magnetic strength.
Answer: False
Match the following
1. Ability of a magnet to attract iron 2. Invisible region around a magnet 3. Process of making a magnet 4. Magnet produced by electricity 5. Natural magnetic rock
1 – Magnetism
2 – Magnetic field
3 – Magnetisation
4 – Electromagnet
5 – Magnetite
Assertion – Reason
1. Assertion: Magnets can attract iron. Reason: Iron is a magnetic substance.
Answer: Both A and R are true and R is the correct explanation.
2. Assertion: A freely suspended bar magnet always points north–south. Reason: The Earth behaves like a giant magnet.
Answer: Both A and R are true and R is the correct explanation.
Subjective Questions
1. Write any five uses of magnets.
• Finding directions using compass
• Electric bells and relays
• Loudspeakers and microphones
• Separation of iron from waste
• Refrigerator and cupboard catches
2. Differentiate between artificial magnets and natural magnets.
Artificial magnets are man-made, stronger and can be made in desired shapes. Natural magnets are found in nature, weaker and have limited shapes.
3. Differentiate between permanent magnets and electromagnets.
Permanent magnets have permanent magnetism and do not need electricity. Electromagnets have temporary magnetism and work only when electricity flows.
4. Write the properties of magnetic field lines.
• They form closed loops
• They never intersect each other
• They are crowded near the poles
• They show direction of magnetic field
5. What are the methods of making a magnet?
• Single touch method
• Double touch method
• Electrical method
• Induction method
6. How are magnets prevented from self-demagnetisation?
Magnets are stored with soft iron keepers across their poles. Bar magnets are stored in pairs with unlike poles together.
Exemplar Problems
1. The needle of a magnetic compass flickers when brought near a mobile phone or TV speaker. Why?
Mobile phones and speakers produce magnetic fields due to electric current. This external magnetic field interferes with the Earth’s magnetic field, causing the compass needle to flicker.
2. A bar magnet and an iron piece are of same size and shape. How will you identify them using: a. Another magnet b. A compass c. A thread
a. Magnet shows repulsion, iron does not.
b. Compass needle deflects near magnet.
c. Magnet aligns north–south when suspended.
