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Two concentric co-planar coils of turns $n_{1}$ and $n_{2}$ have radii ratio $2 : 1$ , respectively. Equal currents in both the coils flow in opposite directions. If net magnetic field is zero at their common centre, then $n_{1} : n_{2}$ is,

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Important Questions on Moving Charges and Magnetism

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A current

i

flows through a loop as shown in figure. The magnetic field at the Centre

O

HARD

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A small circular loop of conducting wire has radius a and carries current

I .

It is placed in a uniform magnetic field

B

perpendicular to its plane such that when rotated slightly about its diameter and released, it starts performing simple harmonic motion of time period

T .

The mass of the loop is

m

then:

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

The magnetic field at the centre of a circular coil of

50

turns and radius

10 cm

carrying a current of

1 A,

in tesla is

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A Helmholtz coil has a pair of loops, each with

N

turns and radius

R

. They are placed coaxially at distance

R

and the same current

I

flows through the loops in the same direction. The magnitude of the magnetic field at

P,

midway between the centres

A

and

C,

is given by [Refer to figure given below]:
Question Image

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

Two infinitely long wires each carrying current

I

along the same direction are made into the geometry as shown in the figure below.
Question Image

The magnetic field at the point

P

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

The coefficient of self-induction of a closely wound coil of

100

turns and area of cross-section

1 {cm}^{2}

1 mH

. Find the magnetic induction at the centre of its core when a current of

2 A

flows in it.

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

The magnetic field at the centre ${}^{'}O^{'}$ in the given figure is

Question Image

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

Magnetic field at the centre of a circular loop of area

A

B

. The magnetic moment of the loop will be (

μ_{0} =

permeability of free space)

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

The magnitude of a magnetic field at the centre of a circular coil of radius

R

, having

N

turns and carrying a current

I

can be doubled by changing

HARD

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

Two identical wires

A

and

B

, each of length

l

, carry the same current

I

. Wire

A

is bent into a circle of radius

R

and wire

B

is bent to form a square of side

a

. If

B_{A}

and

B_{B}

are the values of magnetic field at the centres of the circle and square respectively, then the ratio

\frac{B_{A}}{B_{B}}

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

Let

{\vec{B}}_{1}

is the magnetic field at the centre of the current carrying coil of radius

R

and

{\vec{B}}_{2}

is the magnetic field on the axis of same circular coil at the distance of

3 R .

Then the ratio

\frac{|{\vec{B}}_{1}|}{|{\vec{B}}_{2}|}

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

An electron moving in a circular orbit of radius

r

makes

n

rotations per second. The magnetic field produced at the center has magnitude:

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

Two circular loops

L_{1}

and

L_{2}

of wire carrying equal and opposite currents are placed parallel to each other with a common axis. The radius of loop

L_{1}

R_{1}

and that of

L_{2}

R_{2}

. The distance between the centres of the loops is

\sqrt{3} R_{1}

. The magnetic field at the centre of

L_{2}

shall be zero if

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

The magnetic field at the centre $O$ of the current-carrying square loop shown in the figure is

Question Image

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A circular coil of radius

R

carries an electric current

I

. The magnetic field due to the coil at a point on the axis of the coil located at a distance

r

from the centre of the coil, such that

r ≫ R,

the magnetic field at that point is proportional to

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A circular loop of radius

r

of conducting wire connected with a voltage source of zero internal resistance produces a magnetic field

B

at its centre. If instead, a circular loop of radius

2 r

, made of same material, having the same cross-section is connected to the same voltage source, what will be the magnetic field at its centre?

HARD

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A circular coil connected to a battery of emf

E

produced a certain magnetic induction field at its centre. The coil is unwound, stretched to double its length rewound into a coil of

\frac{1^{rd}}{3}

of the original radius and connected to a battery of emf

E^{'}

to produce same field at the centre. Then

E^{'}

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A thin ring of

10 c m

radius carries a uniformly distributed charge. The ring rotates at a constant angular speed of

40 π r a d s^{- 1}

about its axis, perpendicular to its plane. Is the magnetic field its centre is

3.8 \times 10^{- 9} T

, then the charge carried by the ring is close to

(μ_{0} = 4 π \times 10^{- 7} N A^{- 2}) .

EASY

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A long wire carrying a steady current is bent into a circular loop of one turn. The magnetic field at the centre of the loop is

B .

It is then bent into a circular coil of

n

turns. The magnetic field at the centre of this coil of

n

turns will be

MEDIUM

Physics>Electricity and Magnetism>Moving Charges and Magnetism>Magnetic Field on the Axis of a Circular Current Loop

A circular coil carrying current

I

has a radius

R

and magnetic field at the centre is

B

. The distance from the centre along the axis of the same coil where the magnetic field will be

\frac{B}{8}

Two concentric co-planar coils of turns n1 and n2 have radii ratio 2:1, respectively. Equal currents in both the coils flow in opposite directions. If net magnetic field is zero at their common centre, then n1:n2 is,

Important Questions on Moving Charges and Magnetism

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Two concentric co-planar coils of turns $n_{1}$ and $n_{2}$ have radii ratio $2 : 1$ , respectively. Equal currents in both the coils flow in opposite directions. If net magnetic field is zero at their common centre, then $n_{1} : n_{2}$ is,