Choose the right answer from the following. A constant current I is maintained in a solenoid. Which of the following quantities will not increase if an iron rod is inserted in the solenoid along its axis? (a) the magnetic field at the centre (b) self-inductance of the solenoid (c) magnetic flux linked with the solenoid (d) rate of Joule heating.

Answer: rate of joule heating

Explanation: When an iron rod is inserted inside a solenoid the magnetic field inside the solenoid increases due to the high magnetic permeability of iron. Due to the increased magnetic field, the magnetic flux also increases. The self-inductance of the solenoid also increases because the self-inductance (L) of the coil is directly proportional to the permeability of the material inside the solenoid. The rate of joule heating doesn’t change.