Magnetism and Matter Test 8

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Magnetism and Matter Test 8

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Question 1
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Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
Assertion (A): The magnetic field configuration with 3 poles is not possible.
Reason (R): No torque acts on a bar magnet itself due to its own field.

A
A. Both A and R are true and R is the correct explanation of A

B
B. Both A and R are true but R is NOT the correct explanation of A

C
C. A is true but R is false

D
D. A is false and R is true

Solution

Magnetic poles exist in pairs. So assertion is true. The bar magnet does not exert a torque on itself in its own magnetic field. Torque is proportional to cross product of and .The angle between and being 0, the cross product is 0. So, there will be no torque. So reason is also true. But R cannot explain A.
Question 2
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Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
Assertion (A): The basic difference between magnetic lines of force and electric lines of force is electric lines of force are discontinuous and magnetic lines of force are continuous.
Reason (R): Magnetic lines of force exist in a magnet but no electric lines of force exist in a charged body.

A
A. Both A and R are true and R is the correct explanation of A

B
B. Both A and R are true but R is NOT the correct explanation of A

C
C. A is true but R is false

D
D. A is false and R is true

Solution

Let us consider an electric dipole. The electric lines of force exist outside only and not inside the dipole. Let us take a magnetic dipole. The magnetic lines of force exist outside as well as inside the dipole. So, it can be said that magnetic lines of force are continuous and electric lines of force are discontinuous. So assertion and reason both are true and reason explains the assertion too.
Question 3
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Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
Assertion (A): A compass needle when placed at Earth’s magnetic pole rotates in vertical plane.
Reason (R): The Earth has only horizontal component of its magnetic field at the poles.

A
A. Both A and R are true and R is the correct explanation of A

B
B. Both A and R are true but R is NOT the correct explanation of A

C
C. A is true but R is false

D
D. A is false and R is true

Solution

Magnetic needle can rotate in horizontal plane only. But at poles, there is no horizontal component of Earth’s magnetic field. So, the needle will remain horizontal and will point in any direction. Hence the assertion is false. At poles, Earth has only vertical components of its magnetic field. Hence, the reason is also false.
Question 4
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Directions: In the following questions, A statement of Assertion (A) is followed by a statement of Reason (R). Mark the correct choice as.
Assertion (A): Ferromagnetic substances become paramagnetic beyond Curie temperature.
Reason (R): Domains are destroyed at high temperature.

A
A. Both A and R are true and R is the correct explanation of A

B
B. Both A and R are true but R is NOT the correct explanation of A

C
C. A is true but R is false

D
D. A is false and R is true

Solution

From Curie Weiss law,
As temperature increases beyond Curie temperature, susceptibility decreases and the ferromagnetic substances become paramagnetic. So, the assertion is true. Paramagnetic substance has no magnetic domain. At a very high temperature, the domains of ferromagnetic substance get destroyed and the substance transforms into paramagnetic substance. So, the reason is also true and properly explains the assertion.
Question 5
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Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
Assertion : We cannot think of a magnetic field configuration with three poles
Reason : A bar magnet does exert a torque on itself due to its own field.

A
If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B
If both the Assertion and Reason are incorrect.

C
If the Assertion is correct but Reason is incorrect.

D
If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.If both the Assertion and Reason are incorrect.

Solution

The bar magnet or any other magnet does not exert a torque on itself in its own magnetic field. Torque τ ∝ x. As the magnetic field is due to the magnetic moment the value of cross product will be zero. ∵ θ = 0 Magnetic poles exist in pairs. However one can visualize, theoretically, magnetic field due to three poles formed by placing the north poles of the two magnets in contact and the south poles separated by some distance.
Question 6
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Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
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 rotation of the earth.

A
A. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B
B. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

C
C. If the Assertion is correct but Reason is incorrect.

D
D. If both the Assertion and Reason are incorrect.

Solution

As we know that a compass needle is magnetized and freely suspended to allow that horizontal force to pull it toward the magnetic north by some natural force. Moreover, the Earth's magnet is not perfectly arranged with the geographical north and south poles.
Question 7
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Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
Assertion : Magnetic Resonance Imaging (MRI) is a useful diagnostic tool for producing images of various parts of the human body.
Reason : Protons of various tissues of the human body play a role in MRI.

A
A. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B
B. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

C
C. If the Assertion is correct but Reason is incorrect.

D
D. If both the Assertion and Reason are incorrect.

Solution

MRI is useful diagnostic tool for producing images of various parts of human body because it makes use of magnetic property of spinning proton inside the nucleus.
Question 8
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Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
Assertion : Ferro-magnetic substances become paramagnetic above Curie temp.
Reason : Domains are destroyed at high temperature.

A
A. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B
B. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

C
C. If the Assertion is correct but Reason is incorrect.

D
D. If both the Assertion and Reason are incorrect.

Solution

Susceptibility of ferro magnets decreases with increase of temperature. At a transition temperature called Curie temperature they pass over to paramagnets. When temperature is increased, dipoles acquire kinetic energy and are disoriented, hence domain internal interaction called exchange coupling disappears.
Question 9
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Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
Assertion : The ferromagnetic substance do not obey Curie’s law.
Reason : At Curie point a ferromagnetic substance start behaving as a paramagnetic substance.

A
A. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B
B. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

C
C. If the Assertion is correct but Reason is incorrect.

D
D. If both the Assertion and Reason are incorrect.

Solution

The susceptibility of ferromagnetic substance decreases with the rise of temperature in a complicated manner. After Curie point in the susceptibility of ferromagnetic substance varies inversely with its absolute temperature. Ferromagnetic substance obey's Curie's law only above its Curie point.
Question 10
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Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.
Assertion : A paramagnetic sample display greater magnetisation (for the same magnetic field) when cooled.
Reason : The magnetisation does not depend on temperature.

A
A. If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

B
B. If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.

C
C. If the Assertion is correct but Reason is incorrect.

D
D. If both the Assertion and Reason are incorrect.

Solution

A paramagnetic sample displays greater magnetisation when cooled, this is because at lower temperature, the tendency to disrupt the alignment of dipoles (due to magnetising field) decreases on account of reduced random thermal motion.