Moving Charges and Magnetism Test

Result

Moving Charges and Magnetism Test - 30

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Question 1
1 / -0

An electron moving with velocity 'v' enters a magnetic field as shown in the above figure.
Identify the path followed by the electron ?

A
parabola

B
straight line

C
spiral or helix

D
hyperbola

E
circle

Solution

When the given velocity is resolved into its components, the component of velocity that is perpendicular to magnetic field B is responsible for the magnetic force. This force acts as the centripetal force thereby giving the charge a circular motion.
Whereas the component of the velocity that is along the direction of the magnetic field, drags the charge in its direction.
The overall effect of these motions causes the charge to follow a spiral or helical path.

Therefore option C is correct.
Question 2
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Identify the condition in which charged particle will experience the maximum force:

A
when traveling perpendicular to the magnetic field.

B
when traveling parallel to the magnetic field.

C
when traveling opposite to the magnetic field.

D
when traveling neither parallel nor perpendicular to the magnetic field.

E
when the relative motion is at a maximum.

Solution

Magnetic force $F_m = q vB$ $sin\theta$ where $\theta$ is the angle between $v$ and $B$ .
For magnetic force to be maximum, $sin\theta =1$ $\implies \theta =90^o$
Thus the charge traveling perpendicular to the magnetic field experiences the maximum force.
Question 3
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Three different identical charge particles are pictured in the same magnetic field which points into the screen (represented by blue X's). The particles are moving at the same speeds but in different directions, as indicated by the red arrows.
How do the particles rank. In terms of the force they experience due to their movements in the magnetic field greatest first?

A
1, 2, 3

B
1 and 2 tie, 3

C
3, 1 and 2 tie

D
3, 2, 1

E
all tie,

Solution

The equation for the force on a charged particle moving through a magnetic field IS $F=Bv\sin \theta$
where theta is the angle between the velocity direction and the direction of the magnetic field.If we look carefully at the directions here, we see that the velocity directions are all at ninety degrees to the magnetic field. All velocity directions are in the plane of the screen. The magnetic field direction is perpendicular to the screen.The force that all the charged particles experience is the same.
so correct Choice is option "E"
Question 4
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Two identical straight wires carry current in opposite directions as shown in the figure above. Identify which of the following graphs represents the magnetic force acting on each wire?

A

B

C

D

E
There is no net force acting on either wire

Solution

We know when current flows in opposite directions in two straight, parallel wires, they repel each other. That is shown in fig B.
Question 5
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When a charged particle moves in a magnetic field its kinetic energy __________.

A
Remains constant

B
Increases

C
Can decrease

D
Become zero

Solution

The magnetic force acts perpendicular to the velocity of the particle. This causes circular motion. in magnetic field the speed and kinetic energy of the particle remain constant, but the direction is altered at each instant by the perpendicular magnetic force.
Hence the kinetic energy remains constant. Therefore the correct option is (A).
Question 6
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A charged particle is moving along a magnetic field line. The magnetic force on the particle is

A
Along its velocity

B
Opposite to its velocity

C
Perpendicular to its velocity

D
Zero

Solution

Force on a charged particle in the magnetic field is
F =q(v × B ) or F=qvBsinθ
Here, θ=0 i.e., v is parallel to B

∴ F=0
Question 7
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A charged particle experiences magnetic force in the presence of magnetic field. Which of the following statement is correct?

A
The particle is moving and magnetic field is perpendicular to the velocity.

B
The particle is moving and magnetic field is parallel to velocity.

C
The particle is stationary and magnetic field is perpendicular.

D
The particle is stationary and magnetic field is parallel.

Solution

When charge is placed in a magnetic field it will experience magnetic force if
1) The charge is moving as no magnetic force acts on static charge.
2)Velocity of moving charge has component perpendicular to the direction of magnetic field.
Question 8
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If a charged particle is projected in a region of magnetic field, then :

A
the speed of the charge particle continuously charges

B
a magnetic force on the charged particle must be zero

C
the speed of the charged particle remain constant

D
the magnetic force on the charged particle must not be zero

Solution
Question 9
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A particle of mass m and change q moving with velocity $V { }$ enters a region of uniform magnetic field of induction $B { }$ . Then

A
Its path in the region of the field is always circular

B
Its path in the region of the field is circular if $v { } ,B { } =0$

C
Its path in the region of the field is a straight line if $v{ } \times B{ } =0$

D
Distance travelled by the particle in time T does not depend on the angle between $v{ }$ and $B { }$

Solution

Mass $=m$

Velocity $=v$

Charge $=q$

Now,

Kinetic energy of charged particle will never change whatever b the direction of projection.

$F=q\left( v\times B \right)$

Which means angle between F and v hence between F and d is always ${{90}^{0}}$

Now, work is dot product of F and d is always zero

So, no work done on charged particle by magnetic force so its kinetic energy never change

So,
The magnetic field is perpendicular to velocity, so the particle will perform a uniform circular motion and thus speed will not change and thus no change in kinetic energy.
Question 10
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The direction of the force on a current carrying wire placed in a magnetic field depends on

A
The direction of the current but not on the direction of the field

B
The direction of the field but not on the direction of the current

C
The direction of the current as well as the direction of the field

D
Neither the direction of the current nor the direction of the field,

Solution

Given : The direction of the force on a current carrying wire placed in a magnetic field depends on

Solution :
We have a formula for force on a current carrying wire as
$\vec{F}= l \times ( \vec{i} \times \vec{B})$
here $\vec{i}$ =current vector , $\vec{B}$ = magnectic field vector , l=length

From here we can say that The direction of the force on a current carrying wire placed in a magnetic field depends on the direction of the current and the direction of the field.

The correct opt :C