Question

Inside a long straight uniform wire of circular cross-section there is a long cylindrical cavity 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)Magnetic 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

Magnetic field inside cavity is $\overrightarrow{B}=\frac{{\mu }_0}{2}(\overrightarrow{J}\times \overrightarrow{L})$

Magnetic field inside the cavity is uniform and directly proportional to $L$