Magnetism and Matter & EMI - Revision Session - NEET & AIIMS 2020Contact Number: 9667591930 / 8527521718

Page:

1.

**Assertion** : Two coaxial conducting rings of different radii are placed in space. The mutual inductance of both the rings maximum if the rings are coplanar.

**Reason** : For two coaxial conducting rings of different radii, the magnitude of magnetic flux in one ring due to current in other ring is maximum when both rings are coplanar

2.

**Assertion:** No electric current will be present within a region having a uniform and constant magnetic field.

**Reason:** Within a region of uniform and constant magnetic field $\overrightarrow{\mathrm{B}}$ the path integral of the magnetic field $\mathrm{\phi}\overrightarrow{\mathrm{B}}.\overrightarrow{\mathrm{dl}}$ along any closed path is zero. Hence from ampere circuital law $\mathrm{\phi}\overrightarrow{\mathrm{B}}.\overrightarrow{\mathrm{dl}}={\mathrm{\mu}}_{0}\mathrm{l}$ (where the given terms have usual meaning), no current can be present within a region having a uniform and constant magnetic field.

(1) Statement I is True, Statement II is True, Statement II is correct explanation for Statement I.

(2) Statement I is True, Statement II is True, Statement II is NOT a correct explanation for Statement I.

( 3) Statement I is True, Statement II is false.

( 4) Statement I is False, Statement II is true.

3.

**Assertion**: Two identical circulars closed loops made of copper and aluminium are withdrawn from the magnetic field with equal velocities. The induced emf is same but induced current is different.

**Reason** : Induced current depends on the resistance of the circuit.

4.

**Assertion**: A resistance R is connected between the two ends of parallel smooth conducting rails. A conducting rod lies on these fixed horizontal rails and a uniform constant magnetic field B exists perpendicular to the plane of the rails as shown in the figure. If the rod is given a velocity v and released as shown in the figure, it will stop after some time. The total work done by the magnetic field is negative.

**Reason**: If a force acts opposite to the direction of velocity, its work done is negative.

5.

**Assertion** : The poles of a magnet cannot be separated by breaking into two pieces.

**Reason** : The magnetic moment will be reduced to half when magnet is broken into two equal pieces

6.

**Assertion**: If a compass needle is kept at the magnetic north pole of the earth, the compass needle may stay in any direction.

**Reason** : Dip needle will stay vertical at the north pole of the earth.

7.

**Assertion** : The earth's magnetic field is due to iron present in ts core.

**Reason** : At a high-temperature magnet losses its magnetic property or magnetism.

8.

**Assertion** : The susceptibility of diamagnetic materials does not depend upon temperature.

**Reason** : Every atom of a diamagnetic material is not a complete magnet is itself.

9.

A metallic rod of length is tied to a string of length 21 and made to rotate with angular speed won a horizontal table with one end of the string fixed. If there is a vertical magnetic field 'B' in the region, the e.m.f. induced across the ends of the rod is

1. $\frac{2{\mathrm{B\omega l}}^{2}}{2}$

2. $\frac{3{\mathrm{B\omega l}}^{2}}{2}$

3. $\frac{4{\mathrm{B\omega l}}^{2}}{2}$

4. $\frac{5{\mathrm{B\omega l}}^{2}}{2}$

10.

A simple pendulum with a bob of mass m and conducting wire of L swings under gravity through an angle 2$\mathrm{\theta}$. The earth's magnetic field component in the direction perpendicular to swing is B. Maximum potential difference induced across the pendulum is

1. $2\mathrm{BL}\mathrm{sin}\left(\frac{\mathrm{\theta}}{2}\right){\left(\mathrm{gL}\right)}^{1/2}$

2. $\mathrm{BL}\mathrm{sin}\left(\frac{\mathrm{\theta}}{2}\right)\left(\mathrm{gL}\right)$

3. $\mathrm{BL}\mathrm{sin}\left(\frac{\mathrm{\theta}}{2}\right){\left(\mathrm{gL}\right)}^{3/2}$

4. $\mathrm{BL}\mathrm{sin}\left(\frac{\mathrm{\theta}}{2}\right){\left(\mathrm{gL}\right)}^{2}$

11.

An inductor (L= 100 mH), a resistor (R = 100 $\mathrm{\Omega}$), and a battery (E = 100V) are initially connected in series as shown in the figure. After a long time, the battery is disconnected after short-circuiting the points A and B. The current in circuit 1 ms after the short circuit is

1. 1/A

2. eA

3. 0.1 A

4. 1A

12.

An inductor of inductance L = 400 mH and resistors of resistance of ${\mathrm{R}}_{1}=2\mathrm{\Omega}$ and ${\mathrm{R}}_{2}=2\mathrm{\Omega}$ are connected to a battery of emf 12 V as shown in the figure. The internal resistance of the battery is negligible. The switch S is closed at t = 0. The potential drop across Las function of time is

1. $\frac{12}{\mathrm{t}}{\mathrm{e}}^{-3\mathrm{t}}\mathrm{V}$

2. $6\left(1-{\mathrm{e}}^{-\mathrm{t}/0.2}\right)\mathrm{V}$

3. $12{\mathrm{e}}^{-5\mathrm{t}}\mathrm{V}$

3. $6{\mathrm{e}}^{-5\mathrm{t}}\mathrm{V}$

13.

A dip needle lies initially in the magnetic meridian when it shows an angle of dip $\mathrm{\theta}$ at a place. The dip circle is rotated through an angle x in the horizontal plane and then it shows an angle of dip $\mathrm{\theta}$'. Then $\frac{\mathrm{tan}\mathrm{\theta}\text{'}}{\mathrm{tan}\mathrm{\theta}}$ is

1. 1/cos x

2. 1/sin x

3. 1/tan x

4. cos x

14.

The figure shows the various positions (labelled by subscripts) of small magnetised needles P and Q. The arrows show the direction of their magnetic moment. Which configuration corresponds to the lowest potential energy among all the configurations shown.

(1) PQ_{3}

(2) PQ_{4}

(3) PQ_{5}

(4) PQ_{6}

15.

Two tangent galvanometers A and B have coils of radii 8 cm and 16 cm respectively and resistance 8 $\mathrm{\Omega}$ each. They are connected in parallel with a cell of emf 4 V and negligible internal resistance. The deflections produced in the tangent galvanometers A and B are 30° and 60° respectively. If A has 2 turns, then B must have

1. 18 turns

2. 12 turns

3. 6 turns

4. 2 turns

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