Fun with Magnets Test

Result

Fun with Magnets Test - 3

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Weekly Quiz Competition

Question 1
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Vikram dips a bar magnet into a container of iron filings. Which areas of the bar magnet attract the most amount of iron filings?

A
P and Q

B
P and S

C
R and S

D
P, Q and R

Solution

The strength of a magnet lies at its ends, called poles. So, the ends (P and S) of the bar magnet will attract the most amount of iron filings.
Question 2
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If a magnet is cut into four pieces length-wise, then the number of poles obtained will be

A
4

B
8

C
16

D
2

Solution

Every magnet has two poles. So, when a magnet is cut into four pieces length-wise, eight poles will be obtained.
Each small magnet will have its own north and south pole.
Question 3
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The needle of a compass is made of a magnet because it _____.

(i) attracts metal
(ii) gets deflected when a magnet is brought nearby
(iii) comes to rest in East-West direction
(iv) comes to rest in North-South direction

A
(i) and (ii)

B
(i), (ii) and (iii)

C
(ii) and (iv)

D
(ii) only

Solution

A magnetic compass contains a small magnetic needle or pin which aligns itself along N - S direction, and gets deflected in a magnetic field or when a magnet is brought near it.
Question 4
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In the given diagrams, compasses are used to plot the magnetic field around a bar magnet with poles marked N (North) and S (South). Which of the following diagrams correctly shows the expected field pattern?

A

B

C

D

Solution

Outside the magnet, magnetic field lines travel from North pole towards the South pole, as shown in the figure.
Question 5
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Which of the following statements is/are true?

(a) A magnetic compass has a translucent cover on circular dial.
(b) A compass needle is a magnetised needle.
(c) A compass needle has the same type of poles on both sides.

A
Only (a) and (b)

B
Only (c)

C
Only (b) and (c)

D
Only (b)

Solution

A magnetic compass contains a small magnetic pin or needle which aligns itself along the North -South direction when left undisturbed.
Hence the statement 'b' is correct.
A magnetic compass has a transparent glass cover on circular dial. Hence, statement 'a' is incorrect.
The magnetic needle has a North and a South pole at the opposite ends. Hence, the statement 'c' is incorrect.
Question 6
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The figure below shows a ring magnet X, floating above another ring magnet Y. This is because ___________________.

A
magnet X is lighter than magnet Y

B
magnet Y is more powerful than magnet X

C
like poles of both magnets are facing each other and consequently, there is a repulsive force between them

D
unlike poles of both magnets are facing each other and consequently, there is an attractive force between them

Solution

Like poles of both magnets are facing each other. As a result, they repel each other. The repulsive force of magnet Y will balance the weight of magnet X.
Question 7
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What would happen when a magnet is held near a cork, as shown in the diagram?

A
The cork would move towards the magnet because of magnetic force of repulsion.

B
The cork would move towards the magnet because of magnetic force of attraction.

C
The cork would move away from the magnet because of magnetic force of repulsion.

D
The cork would move away from the magnet because of magnetic force of attraction.

Solution

When a magnet is held near the cork, the cork will move away from the magnet because of magnetic force of repulsion acting between the like poles. Like poles repel each other, while unlike poles attract each other.
Question 8
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What will happen when three bar magnets are hung in the manner shown below?

A
Magnet Y will keep rotating.

B
Magnet Y will move towards magnet Z.

C
Magnet Y will move towards magnet X.

D
None of the magnets will move.

Solution

Like poles repel each other, while unlike poles attract each other. The North pole of magnet Y will be repelled by the North pole of magnet X, and South pole of magnet Y will be attracted by the North pole of magnet Z.
Question 9
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If magnetised iron filings are mixed with soil and a bar of thermocol is placed over it, then what type of force will act between the
thermocol bar and iron filings mixed with the soil?

(a) Strong force of repulsion
(b) No force of attraction
(c) No force of repulsion
(d) Strong force of attraction

A
Only (a)

B
Both (b) and (c)

C
Only (d)

D
Only (b)

Solution

As the thermocol is a non-magnetic substance, so it will not be attracted or repelled by magnetised iron filings.
Question 10
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Which of the following materials is best suited for making magnetic keepers?

A
Wood

B
Steel

C
Iron

D
Alnico

Solution

Magnetic keepers are soft iron bars placed at either end of a pair of magnets. It is used to avoid self-demagnetisation of magnets.
The magnets are arranged in pairs with opposite poles facing each other. Two soft irons are placed at the either end of the pair of magnets.
Question 11
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A student tries to magnetise a short steel rod, and succeeds in doing so. What does he observe?

A
Both ends of the magnet attract the magnetised rod.

B
The magnetised rod picks up a small piece of paper.

C
One end of the magnet repels the magnetised rod.

D
When freely suspended, the magnetised rod does not point in any particular direction.

Solution

When the iron rod is magnetised, one end will behave as the North pole and the other end will behave as the South pole. Now, in case of magnets, like poles repel each other and unlike poles attract each other.
Question 12
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In which of the following cases do magnets lose their property of magnetism?

A
When magnets are dropped in water

B
When magnets are hammered

C
When magnets are stored separated by a piece of wood

D
When magnets are placed in a cold room

Solution

When magnets are hammered, they lose their magnetic property.
Question 13
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A magnet which has lost its magnetic property can be re-magnetised

A
by cooling

B
by heating first and then cooling

C
by cooling first and then heating

D
It cannot be re-magnetised.

Solution

By decreasing the temperature, we can regain the lost magnetic properties of magnetic materials.
Question 14
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You should not store a floppy disk near a magnet because ________.

A
the magnet will rust

B
the magnet will become weaker

C
the data on the disk may be erased

D
the magnet will break the disk

Solution

Floppy disk is a device which stores the data in the form of magnetic field. Hence, it is magnetic in nature.

When a magnet is brought near the floppy, the magnetic field of the magnet can disturb the magnetic field of the floppy, and as a result, the information on the disk can be erased.
Question 15
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Ravi was standing with a magnetic compass in his hand. A bird flew in the direction opposite to the direction in which the compass needle was pointing. In which direction did the bird fly?

A
South

B
Northeast

C
North

D
West

Solution

A magnetic needle always points northwards. Now, the bird flew in a direction opposite to the direction in which the compass needle was pointing, so we can say that the bird flew towards south.
Question 16
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What name is given to the device that makes a strong magnet by passing electricity through a coil of wire wrapped around a block of iron?

A
Electric kettle

B
Crane

C
Solenoid

D
Transformer

Solution

A solenoid is a coil of insulated or enameled wire wound around a rod-shaped form made of iron. It behaves as a magnet when current is passed through it. Solenoid is the generic term for a coil of wire used as an electromagnet. It also refers to any device that converts electrical energy to mechanical energy.
Question 17
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Some heated iron filings get cooled when dipped in water. Which of the following statements is true?

(a) They become non-magnetic due to heating and will not be attracted to a magnet.
(b) They become magnetised and align in a particular direction.
(c) They will still be attracted to a magnet.
(d) Water dissolves away the magnetism of the iron filings, so they are no longer attracted to a magnet.

A
(a) only

B
(b) only

C
(c) only

D
(d) only

Solution

Iron is a magnetic material and always remains a magnetic material irrespective of the number of times it is heated or cooled. Hence, statement (c) is true. It is a magnet that loses its magnetic properties on heating. Iron filings are not magnetised and thus, their magnetic properties do not change on heating. Hence, statement (a) is false. They cannot be magnetised on heating, so statement (b) is false. Magnetism is not some tangible matter that can be dissolved away in water. It is a physical property. Hence, statement (d) is false.
Question 18
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Raman applied force to separate two natural magnets : A and B, but he couldn't separate the magnets.
Which of the following statements is true according to the situation?

A
The force of attraction between the magnets is greater than the applied force.

B
The force of attraction between the magnets is less than the applied force.

C
Once two magnets join, they get fused together at the surface of contact and can never be separated again.

D
None of these

Solution

Since, Raman could not separate two magnets, the force of attraction between the two magnets was probably greater than the applied force.
Hence, option (1) is correct.
Question 19
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Which of the following statements is true if two identical bar magnets are cut into two identical pieces each, such that the first one is cut transverse to its length and the second one is cut along its length?

A
All four bar magnets are equally strong.

B
The bar magnet cut along its length is stronger than the other magnet.

C
The bar magnet cut transverse to its length is stronger than the other magnet.

D
The bar magnet cut transverse to its length loses its magnetism.

Solution

When we cut a magnet along the length, the area of cross-section is reduced. Hence, the magnetic pole strength reduces. So, the magnet which is cut perpendicular to its length is stronger.
Question 20
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A bar magnet is broken into two pieces. Which of the following statements is true about the force between the broken pieces if they face each other with a small separation?

A
There is an electric repulsive force between the broken pieces.

B
There is an electric attractive force between the broken pieces.

C
There is a magnetic repulsive force between the broken pieces.

D
There is a magnetic attractive force between the broken pieces.

Solution

When a bar magnet is broken into two pieces, the broken pieces will behave as two independent magnets, and opposite poles will attract each other.