Question

An electric current passes through a long straight copper wire. At a distance 5 cm from the straight wire, the magnetic field is B. The magnetic field at 20 cm from the straight wire would be

a)B/6.

b) B/4

c). B/3.

D). B/2​

Answer 1

Answer:

b) b/4

Explanation:

a long straight wire,

B= 2πrμ 0

i

and B∝ r1

∴ B 1

B= 50m

⇒ B 1 = 200m

B=4⇒B 1

= B/4