1) The magnetic field at a distance r from a long wire carrying current i is 0.4 tesla. The magnetic field at a distance 2r is A) 0.2tesla B) 0.8tesla C) 0.1tesla D) 1.6 tesla Answer: Option AExplanation:Magnetic field due to long wire, $B = \frac{\mu_{0}i}{2\pi r}$ or $B\propto\frac{1}{r}$ When r is doubled, the magnetic field becomes half, i.e., now the magnetic field will be 0.2T.
