TEXTBOOK EXERCISES
I. Choose the best answer.
1.
A magnet attracts __________.
a) wooden materials
b) any metal
c) copper
d) iron and steel
[Answer: (d) iron and steel]
2.
One of the following is an example for a permanent magnet.
a) Electromagnet 
b) Mumetal
c) Soft iron
d) Neodymium
[Answer: (d) Neodymium]
3. The south pole of a bar magnet and the north pole of a U-shaped magnet will __________.
a) attract each other
b) repel each other
c) neither attract nor repel each
other
d) None of the above
[Answer: (a) attract each other]
4.
The shape of the Earth’s magnetic field resembles that of an imaginary
__________.
a) U-shaped magnet
b) straight conductor carrying
current
c) solenoid coil
d) bar magnet
[Answer: (d) bar magnet]
5.
MRI stands for __________.
a) Magnetic Resonance Imaging
b) Magnetic Running Image
c) Magnetic Radio Imaging
d) Magnetic Radar Imaging
[Answer: (a) Magnetic Resonance Imaging]
6.
A compass is used for __________
a) plotting magnetic lines
b) detection of magnetic field
c) navigation
d) All of these
[Answer: (d) All of these]
II. Fill in the blanks.
1. The magnetic strength is maximum at the poles.
2. A magnet has two magnetic
poles.
3. Magnets are used in dynamos for generating electricity.
4. Electromagnets are used to lift heavy
iron pieces.
5. A freely suspended bar magnet is
always pointing along the geographic north-south direction.
III. Match the following.
1. Magnetite - Magnetic lines
2. A tiny pivoted magnet - Natural
magnet
3. Cobalt - Compass box
4. Closed curves - Ferromagnetic
material
5. Bismuth - Diamagnetic material
Answer:
1. Magnetite - Natural magnet
2. A tiny pivoted magnet - Compass box
3. Cobalt - Ferromagnetic material
4. Closed curves - Magnetic lines
5. Bismuth - Diamagnetic material
IV. Consider the statements given below and choose the correct
option.
a. Both assertion and reason are
true and reason is the correct explanation of assertion.
b. Both assertion and reason are
true, but reason is not the correct explanation of assertion.
c. Assertion is true, but reason is
false.
d. Assertion is false, but reason is
true.
1.
Assertion: Iron filings are
concentrated more at the magnetic poles.
Reason: The magnets are so sharp.
[Answer: (b) Both assertion and reason are true but reason is not the
correct explanation of assertion.]
2. Assertion: The Earth’s magnetic field is due to iron present in its
core.
Reason: At a high temperature a magnet
loses its magnetic property or magnetism.
[Answer: (d) Assertion is false but the reason is true.]
Correct statement: The Earth’s magnetic field is due to the molten charged metallic fluid inside the Earth’s surface.
V. Answer briefly.
1. Define
magnetic field.
Answer: The space around a magnet in which its magnetic effect or influence is
observed.
2.
What is artificial magnet? Give examples.
Answer: Magnets that are made by people in a laboratory or a factory are called
artificial magnets. Eg.: Horse shoe magnet, bar magnet, U-shaped magnet,
cylindrical magnets, disc magnets, ring magnets and electromagnets.
3.
Distinguish between natural and artificial magnets?
Answer:
Natural
Magnets
1. These are found in nature.
2. Have irregular shapes and dimensions.
3. The strength of a natural magnet is well determined and difficult
to change.
4. These are permanent magnets.
5. They have a less usage.
Artificial
Magnets
1. These are man-made magnets.
2. They can be made in different shapes and dimensions.
3. Artificial magnets can be made with required and specific
strength.
4. Their properties are time bound.
5. They have a vast usage in day-to-day life.
4.
Earth acts as a huge bar magnet. Why? Give reasons.
Answer:
(i) A freely suspended magnetic needle at a point on the Earth
comes to rest approximately along the geographical north - south direction.
(ii) This shows that the Earth behaves like a huge magnetic
dipole with its magnetic poles located near its geographical poles.
(iii) The north pole of a magnetic needle approximately points
towards the geographic north (NG).
(iv) The magnetic north pole of the needle is attracted by the
magnetic south pole of the Earth (Sm), which is located at the geographic north
NG.
(v) Also, the magnetic south pole of the needle is
attracted by the magnetic north pole of the Earth (Nm), which is located at the
geographic south SG.
5.
How can you identify non-magnetic materials? Give an example of a non-magnetic
material.
Answer:
(i) Materials which are not attracted by magnets are called
non-magnetic materials.
(ii) Example : Wood, Glass, Rubber, Plastic, Aluminium.
VI. Answer in detail.
1.
List out the uses of magnets.
Answer:
(i) In ancient times, the magnet in the form of‘direction stone’
helped seamen to find the directions during a voyage.
(ii) Nowadays, magnets are used to generate electricity in
dynamos.
(iii) Electromagnets are used in our day-to-day life.
(iv) They are used in electric bells and electric motors.
(v) They are used in loudspeakers and microphones.
(vi) An extremely powerful electromagnet is used in the fast moving
Maglev train to remain floating above the tracks.
(vii) In industries, magnetic conveyor belts are used to sort
out magnetic substances from scraps mixed with non-magnetic substances.
(viii) Magnets are used in computer in its storing devices such
as hard disks.
(ix) In banks, the magnets enable the computers to read the MICR
numbers printed on a cheque.
(x) The tip of the screw drivers are made slightly magnetic so
that the screws remain attached to the tip.
(xi) At hospitals, extremely strong electro magnets are used in
the MRI (Magnetic Resonance Imaging) to scan the specified internal organ.
2.
How will you convert a ‘nail’ into a temporary magnet?
Answer:
(i) Spread some steel pins on a wooden board and bring an iron
nail near them.
(ii) Now, make one of the magnetic poles of the bar magnet touch
one end of the iron nail.
(iii) Slide it along its length in one direction slowly till the
other end is reached.
(iv) Repeat the process, as shown in the diagram, 20 to 30
times.
(v) The magnet has to be moved in one direction only.
(vi) Avoid the swiping of the magnet back and forth.
(vii) Now, bring the iron nail near the steel pins.
(viii) The steel pins stick to the iron nail because nail has
become a temporary magnet.
3.
Write a note on Earth’s magnetism.
Answer:
(i) Earth has been assumed or imagined by the scientists as a
huge magnetic dipole.
(ii) The south pole of the imaginary magnet inside the Earth is
located near the geographic north pole and the north pole of the Earth’s magnet
is located near the geographic south pole.
(iii) The line joining these magnetic poles is called the
magnetic axis.
(iv) The magnetic axis intersects the geographic north pole at a
point called the north geomagnetic pole or northern magnetic pole.
(v) It intersects the geographic south pole at a point called
the south geomagnetic pole or southern magnetic pole. 
(vi) The magnetic axis and the geographical axis (axis of
rotation) do not coincide with each other.
(vii) The cause of the Earth’s magnetism, are as follows.
â–¡ Masses of magnetic substances in the Earth
â–¡ Radiations from the Sun
â–¡ Action of the Moon
VII. Higher Order Thinking Questions.
1.
Though Earth is acting as a huge bar magnet it is not attracting other
ferromagnetic materials. Why? Give reasons.
Answer: Earth is not attracting other ferromagnetic materials because
the magnetic character of ferromagnetic materials is affected by the external
temperature. When they are heated, they become paramagnetic at curie
temperature.
2.
Why it is not advisable to slide a magnet on an iron bar back and forth during
magnetising it?
Answer: It is not advisable to slide a magnet on an iron bar back and forth
because moving it in opposite directions will work to cancel each other out.
3.
Thamizh Dharaga and Sangamithirai were playing with a bar magnet. They put the
magnet down and it broke into four pieces. How many poles will be there?
Answer: Each broken piece behaves like a separate magnet. Therefore, four
pieces will have eight poles.
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