Question

Inside a long straight uniform wire of circular cross - section there is a long cylindrical cavity (bore) of radius r whose axis is parallel to the axis of the wire. Axis of cavity is displaced from the axis of wire by a distance ‘L’ as shown in figure. A direct current J flows through the wire. Then
I) Magnetic field inside the cavity is non-uniform
II) Magnetic field inside the cavity is uniform
III) Field inside the cavity is directly proportional to L
IV) Magnetic field inside the cavity is independent of L

• A. I and IV
• B. I and III
• C. II and IV
• D. II and III

Answer 1

The correct option is D II and III

$\overline{B}=\frac{{\mu }_0}{2}(\overline{j}\times \overline{L})$