Force Acting on Moving Charges - NEET Physics Questions
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Force Acting on Moving Charges

Question 11: easy

A magnetic field:

1. Always exerts a force on a charged particle
2. Never exerts a force on a charged particle
3. Exerts a force, if the charged particle is moving across the magnetic field lines
4. Exerts a force, if the charged particle is moving along the magnetic field lines
View Answer

The magnetic force is given by \(F = qvB\sin\theta\). If the particle moves across the field lines, \(\sin\theta \neq 0\), resulting in a non-zero force.

Question 12: easy

If magnetic field in space is \(1\text{ T } \hat{i}\), electric field is \(10\text{ N/C } \hat{i}\), no gravitational field is present and a charged particle is released from rest from origin, it will:

1. not move at all
2. move in circular path
3. move in a helical path
4. move on a straight line
View Answer

Since the particle starts from rest, its initial magnetic force is zero. The electric field accelerates it along \(\hat{i}\). Because velocity remains parallel to the magnetic field, the magnetic force remains zero, and it continues on a straight line.

Question 13: easy

Statement-1: In an isolated conductor, free electrons keep on moving but no net magnetic force acts on a conductor in a magnetic field.


Statement-2: In a conductor, the average velocity of thermal motion of electrons is zero. Hence no current flows through the conductor.

1. Both Statement-1 and Statement-2 are true and Statement-2 is the correct explanation of Statement-1.
2. Both Statement-1 and Statement-2 are true but Statement-2 is not correct explanation of Statement-1.
3. Statement-1 is true but Statement-2 is false.
4. Statement-1 and Statement-2 are false.
View Answer

The net magnetic force on a current-carrying conductor is given by \(F = I L B\). Since average velocity of thermal motion is zero, current \(I = 0\), resulting in zero net force.

Question 14: easy

If the direction of the initial velocity of a charged particle is neither along nor perpendicular to a uniform magnetic field, then the path of charged particle will be

1. An ellipse
2. A circle
3. A straight line
4. A helix
View Answer

When velocity vector is at an angle \(\theta\) (where \(0^\circ < \theta < 90^\circ\)) to the magnetic field, the component parallel to the field produces linear translation, while the perpendicular component produces circular motion. The combined path is a helix.

Question 15: easy

If a proton has velocity \((2\hat{i} + 3\hat{k})\) m/s and it is subjected to a magnetic field of \(4\hat{i}\) T, then its:

1. Speed will not change
2. Path will not change
3. Velocity will remain same
4. Momentum will remain same
View Answer

Since the magnetic force \(\vec{F} = q(\vec{v} \times \vec{B})\) is always perpendicular to the velocity, the work done is zero. Hence, the kinetic energy and speed remain constant.