Magnetism Test

Result

Magnetism Test - 3

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Question 1
1 / -0

A needle made of bismuth is suspended freely in a magnetic field. The angle which the needle makes with the magnetic field is

A
0°

B
45°

C
90°

D
180°

Solution

Bismuth is a diamagnetic substance. So, when placed in an external magnetic field, it rotates such that its axis becomes perpendicular to the magnetic field.
Question 2
1 / -0

A steel wire of length 'l' has a magnetic moment M. It is bent into a semicircular arc. The new magnetic moment is

A
M

B
2M/π

C
M/π

D
Mπ

Solution

If m is pole strength, then m = M/l

When the wire is bent into a semicircular arc, the separation between the two poles changes from l to 2r, where r is radius of the semicircular arc.

Since l = π r or r = l/π, the new magnetic moment of the stell wire,

M' = m × 2r = M/l × 2l/ π = 2M/π
Question 3
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Directions For Questions

From the statements of Assertion and Reason mark the correct answer from the options.

(a) If both assertion and reason are true, and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If both assertion and reason are false.

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Assertion: Diamagnetic materials can exhibit magnetism.
Reason: Diamagnetic materials have permanent magnetic dipole moment.

A
(a)

B
(b)

C
(c)

D
(d)

Solution

Some materials when placed in an external magnetic field, acquire a very low magnetism in a direction opposite to the field. These materials when brought near the end of a strong magnet, they get repelled. These materials are diamagnetic and this property of materials is called the diamagnetism. This property is generally found in materials in which there are even number of electrons in their atoms (or molecules) and pairs are formed with two electrons. In each pair, the spin of one electron is in direction opposite to the spin of other electron. Hence, the electrons of each pair completely cancel the magnetic moment of each other. Thus, the net magnetic moment of each atom of such material is zero.
Question 4
1 / -0

Directions For Questions

In the following question, a statement of Assertion is given, followed by a corresponding statement of Reason. Of the statements, mark the correct answer as:

(a) If both assertion and reason are true and the reason is the correct explanation of assertion.
(b) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If both assertion and reason are false.

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Assertion: The true geographic north direction is found by using a compass needle.
Reason: The magnetic meridian of the earth is along the axis of its rotation.

A
(a)

B
(b)

C
(c)

D
(d)

Solution

A compass is simply a needle shaped magnet that is mounted so it can rotate freely about a vertical axis. When it is held in a horizontal plane, the north pole end of the needle point, generally, towards the geomagnetic north pole (really a south magnetic pole remember). Thus, true geographic north direction cannot be found by using a compass needle. Now vertical plane passing through the magnetic axis of earths magnet is called magnetic meridian.