Moving Charges and Magnetism Test

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Moving Charges and Magnetism Test - 68

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Weekly Quiz Competition

Question 1
1 / -0

Assertion : If an electron is not deflected while passing through a certain region of space, then only possibility is that there is no magnetic region.
Reason : Force is directly proportional to the magnetic field applied.

A
If both assertion and reason are true and the reason is the correct explanation of the assertion.

B
If both assertion and reason are true but reason is not the correct explanation of the assertion.

C
If assertion is true but reason is false.

D
If the assertion and reason both are false.

E
If assertion is false but reason is true.

Solution

In this case we can not be sure about the absence of the magnetic field because if the electron moving parallel to the direction of magnetic field, the angle between velocity and applied magnetic field is zero $$(F = 0)$$. Then also electron passes without deflection. Also $$F=evB \sin\theta\Rightarrow F\propto B.$$
Question 2
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A proton (or charged particular) moving with velocity $$v$$ is acted upon by electric field $$E$$ and magnetic field $$B$$. The proton will move undeflected if

A
$$E$$ is perpendicular to $$B$$

B
$$E$$ is parallel to $$v$$ and perpendicular to $$B$$

C
$$E, B$$ and $$v$$ are mutually perpendicular and $$v=\dfrac EB$$

D
$$E$$ and $$B$$ both are parallel to $$v$$

Solution

In this case $$|\vec {F_e}|=|\vec {F_m}|$$ and both forces are opposite to each other.
So, $$qE = q(vB)$$
$$or, v = \dfrac{E}{B}$$
Question 3
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The pole piece of the magnet used in a pivoted coil galvanometer are

A
Plane surface of a bar magnet

B
Plane surface of a horse-shoe magnet

C
Cylindrical surface of a bar magnet

D
Cylindrical surface of a horse-shoe magnet

Solution

In a suspended coil galvanometer the strength of the current is not proportional to the deflectionϕ. Hence, the current cannot be read directly. To remove this difficulty, it is necessary that in every position of the coil, the plane of the coil be parallel to the magnetic field. It is for this purpose the coil is suspended between cylindrically cut pole pieces and a soft iron core is placed in the coil without touching it anywhere.
Question 4
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Which of the following statement is true.

A
The presence of a large magnetic flux through a coil maintains a current in the coil if the circuit is continuous

B
A coil of a metal wire kept stationary in a uniform magnetic field an e.m.f include in it

C
A charged particle enters a region of uniform magnetic field at an angle $$85^o$$ to the magnetic lines of force, the path of the particles is a circle

D
There is no change in the energy of a charged particle moving in a magnetic field although a magnetic force is acting on it

Solution

When charged particle enters perpendicularly in a magnetic field,it moves on a circular path with a constant speed. Hence it's kinetic energy also remains constant.
Question 5
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A proton and an electron both moving with the same velocity $$v$$ enter into a region of magnetic field directed perpendicular to the velocity of the particles. They will now move in circular orbits such that

A
Their time periods will be same

B
Their time periods for proton will be higher

C
Their time periods for electron will be higher

D
their orbital radii will be same

Solution

We know that period $$T=\dfrac {2\pi m}{qB}$$ i.e., $$T\propto m$$
(Since $$q$$ and $$B$$ are same)
$$\because $$ Mass of proton > Mass of electron
$$\therefore$$ Time period of proton > Time period of electron.
Question 6
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If a proton, deutron and $$\alpha-$$particle or being accelerated by the same potential difference enters perpendicular to the magnetic field, then the ratio of their kinetic energy is

A
$$1:2:2$$

B
$$2:2:1$$

C
$$1:2:1$$

D
$$1:1:2$$

Solution

Kinetic energy is magnetic field remains constant ant it is
$$K=q\ V$$

$$\Rightarrow K\propto q (V= constant)$$

$$\therefore K_p: K_d : K_\alpha =q_p :q_d : q_\alpha =1:1:2$$
Question 7
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Two parallel conductors $$A$$ and $$B$$ equal length carry currents $$I$$ and $$10\ I$$, respectively, in the same direction. Then

A
$$A$$ and $$B$$ repel each other with same face.

B
$$A$$ and $$B$$ attract each other with same face.

C
$$A$$ will attract $$B$$, but $$B$$ will repel $$A$$

D
$$A$$ and $$B$$ attract each other with difference face.

Solution

By Fleming left hand rule. we can see that if current flow is same direction then their Force direct to each other i.e they will attract each other.
Question 8
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If a particle of charge $$10^{-12}$$ coulomb moving along the $$\hat x-$$direction with a velocity $$10^5 m/s$$ experiences a force of $$10^{-10}$$ newton in $$\hat y-$$direction due to magnitude field, then the minimum magnitude field is

A
$$6.25\times 10^3$$ tesla in $$\hat z-$$direction

B
$$10^{-15}$$ tesla in $$\hat z-$$direction

C
$$6.25\times 10^{-3}$$ tesla in $$\hat z-$$direction

D
$$10^{-3}$$ tesla in $$\hat z-$$direction

Solution

The force due to the magnetic field is:
$$F=qvB \sin \theta $$

$$\Rightarrow B=\dfrac {F}{qv\sin \theta}$$

$$B_{min}=\dfrac {F}{qv}$$ (when $$\theta =90^o$$)

$$\therefore B_{min}=\dfrac {F}{qv}=\dfrac {10^{-10}}{10^{-12}\times 10^5}=10^{-3}$$ Tesla $$\hat z$$ direction.
Question 9
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A long wire $$A$$ carries current of $$10\ amp$$. Another long wire $$B$$. Which is parallel to $$A$$ and separated by $$0.1\ m$$ from $$A$$, carries a current of $$5\ amp$$, in the opposite direction to that in $$A$$. What is the magnitude and nature of the force experiment per unit length of $$B$$ $$(\mu_0=4 \pi \times 10^{-7}\ weber/amp-m)$$

A
Repulsion force of $$10^{-4} N/m$$

B
Attractive force of $$10^{-4} N/m$$

C
Repulsion force of $$2 \pi \times 10^{-5} N/m$$

D
Attractive force of $$2 \pi \times 10^{-5} N/m$$

Solution

$$F=\dfrac{\mu_0}{4 \pi} \dfrac{2 i_1 i_2}{a}=10^{-7}
\times \dfrac{2 \times 10 \times 5}{0.1}=10^{-4}\ N$$
As the direction in the two wires are opposite, so the force will be Repulsive.
Question 10
1 / -0

A straight conductor carries a current of $$5\ A$$ An electron travelling with a $$10^6 ms^{-1}$$ parallel to the wire at a distance of $$0.1\ m$$ from the conductor, experience a force of

A
$$8 \times 10^{-20} \ N$$

B
$$3.3 \times 10^{-19} \ N$$

C
$$8 \times 10^{-18} \ N$$

D
$$1.6 \times 10^{-19} \ N$$

Solution

Magnetic field produced by wire is perpendicular to the motion of electron and it given by
$$B=\dfrac{\mu_0}{4 \pi}.\dfrac{2i}{a}=10^{-7} \times \dfrac{2 \times 5}{0.1}=10^{-5}\ Wb/m^2$$
Hence force on electron
$$F=qvB=(1.6 \times 10^{-19}) \times 5 \times 10^6 \times 10^{-5}=8 \times 10^{-18} \ N$$

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Moving Charges and Magnetism Test - 68

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Question 1

If both assertion and reason are true and the reason is the correct explanation of the assertion.

If both assertion and reason are true but reason is not the correct explanation of the assertion.

If assertion is true but reason is false.

If the assertion and reason both are false.

If assertion is false but reason is true.

Solution

Question 2

$$E$$ is perpendicular to $$B$$

$$E$$ is parallel to $$v$$ and perpendicular to $$B$$

$$E, B$$ and $$v$$ are mutually perpendicular and $$v=\dfrac EB$$

$$E$$ and $$B$$ both are parallel to $$v$$

Solution

Question 3

Plane surface of a bar magnet

Plane surface of a horse-shoe magnet

Cylindrical surface of a bar magnet

Cylindrical surface of a horse-shoe magnet

Solution

Question 4

The presence of a large magnetic flux through a coil maintains a current in the coil if the circuit is continuous

A coil of a metal wire kept stationary in a uniform magnetic field an e.m.f include in it

A charged particle enters a region of uniform magnetic field at an angle $$85^o$$ to the magnetic lines of force, the path of the particles is a circle

There is no change in the energy of a charged particle moving in a magnetic field although a magnetic force is acting on it

Solution

Question 5

Their time periods will be same

Their time periods for proton will be higher

Their time periods for electron will be higher

their orbital radii will be same

Solution

Question 6

$$1:2:2$$

$$2:2:1$$

$$1:2:1$$

$$1:1:2$$

Solution

Question 7

$$A$$ and $$B$$ repel each other with same face.

$$A$$ and $$B$$ attract each other with same face.

$$A$$ will attract $$B$$, but $$B$$ will repel $$A$$

$$A$$ and $$B$$ attract each other with difference face.

Solution

Question 8

$$6.25\times 10^3$$ tesla in $$\hat z-$$direction

$$10^{-15}$$ tesla in $$\hat z-$$direction

$$6.25\times 10^{-3}$$ tesla in $$\hat z-$$direction

$$10^{-3}$$ tesla in $$\hat z-$$direction

Solution

Question 9

Repulsion force of $$10^{-4} N/m$$

Attractive force of $$10^{-4} N/m$$

Repulsion force of $$2 \pi \times 10^{-5} N/m$$

Attractive force of $$2 \pi \times 10^{-5} N/m$$

Solution

Question 10

$$8 \times 10^{-20} \ N$$

$$3.3 \times 10^{-19} \ N$$

$$8 \times 10^{-18} \ N$$

$$1.6 \times 10^{-19} \ N$$

Solution

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