Question

A positive charge enters a magnetic field and travels parallel to the magnetic field. The charge experiences

• A. an upward force
• B. a downward force
• C. a force in the direction of magnetic field.
• D. no force

Hint:

Force is \(qvB\sin\theta\) and \(\theta = 0\) here.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A moving charge in a magnetic field feels the Lorentz force \(\vec{F} = q(\vec{v}\times\vec{B})\).

Step 2: Apply to parallel motion:
The velocity is parallel to the field, so the angle between them is \(\theta = 0^\circ\). The magnitude is \[ F = qvB\sin 0^\circ = 0 \]

Step 3: Why the other options fail:
Any force from a magnetic field is perpendicular to both \(\vec{v}\) and \(\vec{B}\). So a force along the field (option 3) is never possible. An upward or downward force (options 1 and 2) needs a nonzero cross product, which is zero here.

Final Answer:
The charge feels no force. \[ \boxed{\text{No force}} \]