Force Acting on Moving Charges

Practice Questions:

Question 1: moderate

An electric field E and a magnetic field B applied on a proton which moves with velocity v, it goes undeflected through the region if :

1. E ⊥ B

2. E is parallel to v and perpendicular to B

3. E, B and v all three mutually perpendicular to each other and v = E/B

4. E and B both are parallel but perpendicular to v

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Question 2: easy

A proton, deutron and α-particle are accelerated by same potential, enters in uniform
magnetic field perpendicularly. Ratio of radii of circular path respectively :

1. 1: √2 : √2

2. 2 : 2 : 1

3. 1 : 2 : 1

4. 1 : 1 : 1

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Question 3: difficult

An electron \left(mass = 9.1\times 10^{-31}kg; Charge=-1.6\times 10^{-19}C \right) experiences no deflection if subjected to an electric field of \[3.2\times 10^{5} V/m\] and a magnetic field of 2.0 × 10-³ Wb/m² . Both the fields are normal to the path of electron and to each other . If the electric field is removed, then the electron will revolve in an orbit of radius:

1. 45 m

2. 4.5 m

3. 0.45 m

4. 0.045 m

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Question 4: moderate

A particle having charge of 1 C, mass 1 kg and speed 1 m/s enters a uniform magnetic field, having magnetic induction of 1 T, at an angle θ = 30° between velocity vector and magnetic induction. The pitch of its helical path is (in meters)

1. \[\frac{\sqrt{3}\pi}{2}\]

2. \[\sqrt{3}\pi\]

3. π/2

4. π

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Question 5: moderate

An electron moves in the plane of the page through two regions of space along the
dotted-line trajectory shown in the figure. There is a uniform electric field in Region-I directed
into the plane of the page (as shown). There is no electric field in Region-II. What is a
necessary direction of the magnetic field in regions I and II ? Ignore gravitational forces.

1. Region-I Down the plane of the page Region-II Up the plane of the page

2. Region-I Up the plane of the page Region-II Into the plane of the page

3. Region-I Up the plane of the page Region-II Out of the plane of the page

4. Region-I Down the plane of the page Region-II Out of the plane of the page

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Question 6: easy

Two particles X and Y having equal charges, after being accelerated through the same potential
difference, enter a region of uniform magnetic field and describe circular paths of radii R1 and
R2 respectively. The ratio of masses of X and Y is :

1. \[\left( R_{1}/R_{2} \right)^{1/2}\]

2. \[\left( R_{2}/R_{1} \right)\]

3. \[\left( R_{1}/R_{2} \right)^{2}\]

4. \[\left( R_{1}/R_{2} \right)\]

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Question 7: easy

A beam of electrons is projected horizontally to the right. A straight conductor carrying a current is supported parallel to the electron beam and above it. If the current in the conductor is from left to right, what will be the effect on the electron beam ?

1. The electron beam will be pulled upwards

2. The electron beam will be pulled downwards

3. The electron beam will be retarded

4. The electron beam will be speeded up towards the right

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Question 8: easy

A uniform electric field and a uniform magnetic field are produced, pointed in the same direction. An electron is projected with its velocity pointed in the same direction :

1. the electron will turn to its right

2. the electron will turn to its left

3. the electron velocity will increase in magnitude

4. the electron velocity will decrease in magnitude

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Question 9: easy

An electron moving with a speed u along the positive x-axis at y = 0 enters in a region of
uniform magnetic field \[\overrightarrow{B}=-B_{0}\hat{k}\] which exists to
the right of y-axis. The electron exits from the region after some time with speed v at coordinate
y, then :

1. v > u, y < 0

2. v = u, y > 0

3. v > u, y > 0

4. v = u, y < 0

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Question 10: easy

When a charged particle moving with velocity \(\overrightarrow{v}\)is subjected to a magnetic field of induction \(\overrightarrow{B}\) , the force on it is non-zero. This implies the :

1. angle between \[\overrightarrow{v}\] and \[\overrightarrow{B}\] is necessary 90º

2. angle between \[\overrightarrow{v}\] and \[\overrightarrow{B}\] can have at value other than 90º

3. angle between \[\overrightarrow{v}\] and \[\overrightarrow{B}\] can have at value other than zero and 180º

4. angle between \[\overrightarrow{v}\] and \[\overrightarrow{B}\] is either zero or 180º

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