A positively charged particle is released from rest in a uniform electric field. Its subsequent motion is best described as:

A positively charged particle is released from rest in a uniform electric field. Its subsequent motion is best described as:

• A. It remains at rest
• B. It moves with a constant velocity
• C. It accelerates and then decelerates
• D. It moves with constant acceleration

Answer: (D)

A uniform electric field gives a constant force on a charged particle, F = qE. By Newton’s second law, the acceleration a = F/m = qE/m is constant in both magnitude and direction. If the particle starts from rest, its velocity grows linearly with time: v(t) = (qE/m) t, and it covers distance x(t) = (1/2)(qE/m) t^2 along the field direction. Since the acceleration remains the same and doesn’t change sign, the motion is described as moving with constant acceleration. The other possibilities would require the force (and thus acceleration) to be zero or to vary with time, which doesn’t happen in a uniform field.

A uniform electric field gives a constant force on a charged particle, F = qE. By Newton’s second law, the acceleration a = F/m = qE/m is constant in both magnitude and direction. If the particle starts from rest, its velocity grows linearly with time: v(t) = (qE/m) t, and it covers distance x(t) = (1/2)(qE/m) t^2 along the field direction. Since the acceleration remains the same and doesn’t change sign, the motion is described as moving with constant acceleration. The other possibilities would require the force (and thus acceleration) to be zero or to vary with time, which doesn’t happen in a uniform field.