When a current I is set up in a wire of radius r, the drift speed is vd. If the same current is set up through a wire of radius 2r, then the drift speed will be
A. vd/4
B. vd/2
C. 2vd
D. 4vd
Answer:A
When a current I is set up in a wire of radius r, the drift speed is vd. If the same current is set up through a wire of radius 2r, then the drift speed will be
A. vd/4 B. vd/2 C. 2vd D. 4vd