The acceleration of a particle changes whenA. Direction of velocity changesB. Magnitude of velocity changesC. Either of aboveD. Speed is constant

The correct option is A. Direction of velocity changes.

Acceleration is defined as the rate of change of velocity with respect to time. It is a vector quantity that has both magnitude and direction. When the direction of velocity changes, it means that the particle is changing its path or turning. In this case, the velocity vector is changing, and therefore, the acceleration is nonzero. The acceleration vector will point towards the direction of the change in velocity.

Option B is incorrect because the magnitude of velocity can change without affecting the acceleration. If the magnitude of velocity changes while the direction remains constant (for example, speeding up or slowing down along a straight line), the acceleration will still be nonzero.

Option C is incorrect because it is not true that either of the above conditions (changes in direction or changes in magnitude of velocity) will result in a change in acceleration. The only condition that guarantees a change in acceleration is when the direction of velocity changes.

Option D is incorrect because even if the speed (magnitude of velocity) is constant, the acceleration can still be nonzero if the direction of velocity changes.