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An electric current passes through a lon...

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

A

`B/2`

B

`B/3`

C

`B/4`

D

`B/5`

Text Solution

Verified by Experts

The correct Answer is:
C
`B=(mu_(0))/(4pi)((2I)/(d)) i.le. B prop 1/d`
`therefore(B_(2))/(B_(1))=(d_(1))/(d_(2))=5/20=1/4 therefore B_(2) =B/4`
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