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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - JEE MCQ


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30 Questions MCQ Test Chapter-wise Tests for JEE Main & Advanced - Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 1

Advanced countries are making use of powerful electromagnets to move trains at very high speed. These trains are called maglev trains (abbreviated from magnetic levitation). These trains float on a guideway and  do not run on steel rail tracks.Instead of using a engine based on fossil fuels, they make use of magnetic field forces. The magnetized coils are arranged in the guide way which repels the strong magnets placed in the train's under carriage. This helps train move over the guideway , a technic called electro-dynamic suspension. When current passes in the coils of guideway , a typical magnetic field is set up between the undercarriage of train and guideway which pushes and pull the train along the guideway depending on the requirement.The lack of friction and its aerodynamic style allows the train to more at very high speed.

Q.1. The levitation of the train is due to

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 1

The magnetised coils running along the track repel large magnets on the train's under carriage.

*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 2

Advanced countries are making use of powerful electromagnets to move trains at very high speed. These trains are called maglev trains (abbreviated from magnetic levitation). These trains float on a guideway and  do not run on steel rail tracks.Instead of using a engine based on fossil fuels, they make use of magnetic field forces. The magnetized coils are arranged in the guide way which repels the strong magnets placed in the train's under carriage. This helps train move over the guideway , a technic called electro-dynamic suspension. When current passes in the coils of guideway , a typical magnetic field is set up between the undercarriage of train and guideway which pushes and pull the train along the guideway depending on the requirement.The lack of friction and its aerodynamic style allows the train to more at very high speed.

Q.2. The disadvantage of maglev trains is that

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 2

Initial cost will be more.

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*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 3

Advanced countries are making use of powerful electromagnets to move trains at very high speed. These trains are called maglev trains (abbreviated from magnetic levitation). These trains float on a guideway and  do not run on steel rail tracks.Instead of using a engine based on fossil fuels, they make use of magnetic field forces. The magnetized coils are arranged in the guide way which repels the strong magnets placed in the train's under carriage. This helps train move over the guideway , a technic called electro-dynamic suspension. When current passes in the coils of guideway , a typical magnetic field is set up between the undercarriage of train and guideway which pushes and pull the train along the guideway depending on the requirement.The lack of friction and its aerodynamic style allows the train to more at very high speed.

Q.3. The force which makes maglev move

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 3

The magnetic force will pull the vehicle.

*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 4

The figure shows a circular loop of radius a with two long parallel wires (numbered 1 and 2) all in the plane of the paper. The distance of each wire from the centre of the loop is d. The loop and the wire are carrying the same current I.The current in the loop is in the counterclockwise direction if seen from above.

(q) The magnetic fields (B) at P due to the currents in the wires are in opposite directions.

(r) There is no magnetic field at P.

(s) The wires repel each other.

Q.4.When d ≈ a but wires are not touching the loop, it is found that the net magnetic field on the axis of the loop is zero at a height h above the loop. In that case 

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 4

Magnetic field due to current carrying loop = Magnetic field due to straight wires

B = B1cos θ + B2cos θ = 2 B1cos θ

The current is from P to Q in wire 1 and from R to S in wire 2.

*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 5

The figure shows a circular loop of radius a with two long parallel wires (numbered 1 and 2) all in the plane of the paper. The distance of each wire from the centre of the loop is d. The loop and the wire are carrying the same current I.The current in the loop is in the counterclockwise direction if seen from above.

(q) The magnetic fields (B) at P due to the currents in the wires are in opposite directions.

(r) There is no magnetic field at P.

(s) The wires repel each other.

Q.5. Consider d >> a, and the loop is rotated about its diameter parallel to the wires by 30° from the position shown in the figure. If the currents in the wires are in the opposite directions, the torque on the loop at its new position will be (assume that the net field due to the wires is constant over the loop).

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 5

We know that torque

 

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 6

In a thin rectangular metallic strip a constant current I flows along the positive x-direction, as shown in the figure. The length, width and thickness of the strip are l, w and d, respectively.A uniform magnetic field is applied on the strip along the positive y-direction. Due to this, the charge carriers experience a net deflection along the z-direction. This results in accumulation of charge carriers on the surface PQRS and appearance of equal and opposite charges on the face opposite to PQRS. A potential difference along the z-direction is thus developed. Charge accumulation continues until the magnetic force is balanced by the electric force. The current is assumed to be uniformly distributed on the cross-section of the strip and carried by electrons.

Q.6. Consider two different metallic strips (1 and 2) of the same material. Their lengths are the same, widths are w1 and w2 and thicknesses are d1 and d2 respectively. Two points K and M are symmetrically located on the opposite faces parallel to the x-y plane (see figure). V1 and V2 are the potential differences between K and M in strips 1 and 2, respectively. Then, for a given current I flowing through them in a given magnetic field strength B, the correct statement(s) is(are)

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 6

When megnetic force balances electric force FB = FE
q vd B = q E

   

when d1 = 2d2, V2 = 2V1

and when d1 = d2, V2 = V1 (a), (d) are correct options

 

*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 7

In a thin rectangular metallic strip a constant current I flows along the positive x-direction, as shown in the figure. The length, width and thickness of the strip are l, w and d, respectively.A uniform magnetic field  is applied on the strip along the positive y-direction. Due to this, the charge carriers experience a net deflection along the z-direction. This results in accumulation of charge carriers on the surface PQRS and appearance of equal and opposite charges on the face opposite to PQRS. A potential difference along the z-direction is thus developed. Charge accumulation continues until the magnetic force is balanced by the electric force. The current is assumed to be uniformly distributed on the cross-section of the strip and carried by electrons.

Q.7. Consider two different metallic strips (1 and 2) of same dimensions (length l, width w and thickness d) with carrier densities n1 and n2, respectively. Strip 1 is placed in magnetic field B1 and strip 2 is placed in magnetic field B2, both along positive y-directions. Then V1 and V2 are the potential differences developed between K and M in strips 1 and 2, respectively. Assuming that the current I is the same for both the strips, the correct option(s) is(are)

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 7

Here

A and C are the correct options.

*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 8

Statement-1 : The sensitivity of a moving coil galvanometer is increased by placing a suitable magnetic material as a core inside the coil. and Statement-2 : Soft iron has a high magnetic permeability and cannot be easily magnetized or demagnetized. 

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 8

Statemen t-1 is tr ue. Sensitivity =. If  B increases, θ/I
increases. Statement-2 is wrong because soft  iron can be easily magnetised and de magnetized.

 

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 9

If in a circular coil A of radius R, current I is flowing and in another coil B of radius 2R a current 2I is flowing, then the ratio of the magnetic fields BA and BB, produced by them will be

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 9

KEY CONCEPT : We know that the magnetic field produced by a current carrying circular coil of radius r at its centre is 

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 10

If an electron and a proton having same momenta enter perpendicular to a magnetic field, then 

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 10

KEY CONCEPT : When a charged particle enters perpendicular to a magnetic field, then it moves in a circular path of radius.

where q = Charge of the particle

p = Momentum of the particle

B = Magnetic field

Here p, q and B are constant for electron and proton, therefore the radius will be same.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 11

Wires 1 and 2 carrying currents i1 and i2 respectively are inclined at an angle θ to each other. What is the force on a small element dl of wire 2 at a distance of r from wire 1 (as shown in figure) due to the magnetic field of wire 1? 

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 11

Magnetic field due to current in wire 1 at point P distant r from the wire is

 (directed perpendicular to the plane  of paper, inwards)

The force exerted due to this magnetic field on current element i2 dl is

dF = i2 dl B sin 90°

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 12

The time period of a charged particle undergoing a circular motion in a uniform magnetic field is independent of its

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 12

KEY CONCEPT : The time period of a charged particle (m, q) moving in a magnetic field (B) is T= 2πm/qB
The time period does not depend on the speed of the particle.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 13

A particle of mass M and charge Q moving with velocity describe a circular path of radius R when subjected to a uniform transverse magnetic field of  induction B. The work done by the field when the  particle completes one full circle is

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 13

The workdone,  dW = Fds cosθ The angle between force and displacement is 90° .
Therefore work done is zero.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 14

A particle of charge - 16 *10 -18 coulomb moving with velocity 10ms-1 along  the x-axis enters a region where a magnetic field of induction B is along  the y-axis, and an electric field of magnitude 10 4 V / m is along the negative z-axis. If the charged particle continues moving along the x-axis, the magnitude of  B is

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 14

The situation is shown in the figure.
FE= Force due to electric field FB = Force due to magnetic field It is given that the charged particle remains moving along X-axis (i.e. undeviated). Therefore  FB = FE

*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 15

A thin rectangular magnet suspended freely has a  period of oscillation equal to T. Now it is broken into two equal halves (each having half of the original   length) and one piece is made to oscillate freely in the same field. If its period of oscillation is T ' , the ratio T '/T is

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 15

KEY CONCEPT : The time period of a rectangular magnet oscillating in earth’s magnetic field is given by

where I = Moment of inertia of the rectangular magnetm

μ= Magnetic moment

BH = Horizontal component of the earth’s  magnetic field

Case 2 : Magnet is cut into two identical pieces such that each piece has half the original length. Then

*Multiple options can be correct
Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 16

A magnetic needle lying parallel to a magnetic field requiers W units of work to turn it through 600 . The torque needed to maintain the needle in this position will be

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 16

W = MB(cos θ1 - cosθ2 )

= MB(cos 0° - cos 60°) 

 

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 17

The magnetic lines of force inside a bar magnet       

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 17

As shown in the figure, the magnetic lines of force are directed from south to north inside a bar magnet.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 18

Curie temperature is the temperature above which

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 18

KEY CONCEPT : The temperature above which a ferromagnetic substance becomes paramagnetic is called Curie’s temperature.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 19

A current i ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 19

Using Ampere’s law at a distance r from axis, B is same from symmetry.

Here i is zero, for r < R, whereas R is the radius

∴B = 0

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 20

A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 20

KEY CONCEPT : Magentic field at the centre of a circular coil of radius R carrying current i is 

Given : n ´ (2pr ') =2pR

⇒ nr '=R ...(1)

from (1) and (2), 

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 21

The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is 54 μT. What will be its value at the centre of loop?

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 21

The magnetic field at a point on the axis of a circular loop at a distance x from centre is,

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 22

Two long conductors, separated by a distance d carry current I1 and I2 in the same direction. They exert a force F on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3d. The new value of the force between them is

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 22

Force between two long conductor carrying current,

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 23

The length of a magnet is large compared to its width and breadth. The time period of its oscillation in a vibration magnetometer is 2s. The magnet is cut along its length into three equal parts and these parts are then placed on each other with their like poles together. The time period of this combination will be

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 23

When the magnet is cut into three pieces the pole strength will remain the same and

We have, Magnetic moment (M) = Pole strength (m) × l

∴  New magnetic moment,

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 24

The materials suitable for making electromagnets should have

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 24

NOTE : Electr o mag n et sh ould be amen abl e to magnetisation &  demagnetization.

∴ retentivity should be low & coercivity should be low

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 25

Two concentric coils each of radius equal to 2 π cm are placed at right angles to each other. 3 ampere and 4 ampere are the currents flowing in each coil respectively. The magnetic induction in Weber / m2 at the centre of the coils will be

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 25

The magnetic field due to circular coil 1 and 2 are

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 26

A charged particle of mass m and charge q travels on a circular path of radius r that is perpendicular to a magnetic field B. The time taken by the particle to complete one revolution is

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 26

Equating magnetic force to centripetal force,

Time to complete one revolution,

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 27

A magnetic needle is kept in a non-uniform magnetic field. It experiences 

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 27

A magnetic needle kept in non uniform magnetic field experience a force and torque due to unequal forces acting on poles.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 28

A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity then 

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 28

Due to electric field, it experiences force and decelerates i.e. its velocity decreases.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 29

Needles N1, N2 and N3 are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 29

Ferromagnetic substance has magnetic domains whereas paramagnetic substances have magnetic dipoles which get attracted to a magnetic field.
Diamagnetic substances do not have magnetic dipole but in the presence of external magnetic field due to their orbital motion of electrons these substances are repelled.

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Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 30

In a region, steady and uniform electric and magnetic fields are present. These two fields are parallel to each other. A charged particle is released from rest in this region. The path of the particle will be a

Detailed Solution for Test: JEE Main 35 Year PYQs- Moving Charges & Magnetism - Question 30

The charged particle will move along the lines of electric field (and magnetic field). Magnetic field will exert no force. The force by electric field will be along the lines of uniform electric field. Hence the particle will move in a straight line.

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