Answer: Tangential Velocity
The tangential velocity 
is defined as the angular velocity 
by the radius 
of circular motion. As shown below:
Its name is due to the fact that this linear velocity vector is always tangent to the trajectory and is the distance traveled by a body or object in a circular movement in a period of time.
Answer: The correct answer is a.
Explanation:
Electromagnetic wave is a wave in which the magnetic field and the electric field are perpendicular to each other.
Both fields are directed in the direction of the propagation of the electromagnetic wave. It travels with the speed of the light.
The motion of the electric field produces both electric field and the magnetic field.
The electromagnetic waves are produced when an electric charge vibrates or accelerates.
Therefore, the correct option is (a).
A, C, and D are true when a light spot appears, so those are false.
The answer is therefore B.
