Question

A charged particle is released from rest in a region of space in which steady and uniform electric and magnetic fields are parallel to each other. The particle will move in a

• A. Helix
• B. Straight line
• C. Cycloid
• D. Circle

Hint:

If velocity is parallel to magnetic field, magnetic force becomes zero → motion is governed only by electric field.

Answer 1

The Correct Option is B

Step 1: Forces acting on particle.
The particle experiences electric force and magnetic force.
\[ F_E = qE, \quad F_B = qvB\sin\theta \]

Step 2: Initial condition.
Particle is released from rest, so initially velocity \(v = 0\).
\[ F_B = 0 \]

Step 3: Effect of electric field.
Only electric force acts initially, so particle accelerates in direction of electric field.

Step 4: Direction of magnetic field.
Electric field and magnetic field are parallel, so velocity develops along the same direction as magnetic field.

Step 5: Magnetic force condition.
\[ F_B = qvB\sin 0^\circ = 0 \]
Thus, magnetic force remains zero always.

Step 6: Nature of motion.
Since only electric force acts in a fixed direction, motion remains along a straight line.

Step 7: Final conclusion.
\[ \boxed{\text{Straight line}} \] Hence, correct answer is option (B).