Question

A negatively charged particle initially at rest is placed in an electric field that varies from point to point. There are no other fields. Then :

• A. the particle will move along the electric line of force passing through it
• B. the particle will move opposite to the electric line of force passing through it
• C. the direction of acceleration of the particle will be tangential to the electric line of force at every instant
• D. the direction of acceleration of the particle will be normal to the electric line of force at every instant

Answer 1

Answer: (C)

Answer is C.

As a general rule in electrostatics, electric field lines point in the direction of decreasing electric potential. If a negative charge is initially at rest in an electric field, it will tend to move opposite to the electric field($\overrightarrow{F}=q\overrightarrow{E}$, where, F is the force vector, q is the charge, and E is the electric field vector). Therefore, a negative charge naturally moves in the direction of increasing potential.

A charge in a pure electric field will follow the tangent of an electric field line.

Therefore, the direction of acceleration of the particle is tangential to the electric line of force at every instant.