question_answer

An electric current passes through a long straight wire. At a distance 5 cm from the wire, The magnetic field is B. The field at 20 cm  from the wire would be     [CPMT 2001; Pb PET 2002]

A)            \[\frac{B}{6}\]                     

B)            \[\frac{B}{4}\]

C)            \[\frac{B}{3}\]                     

D)            \[\frac{B}{2}\]