Solenoids And Toroids

Step 1: Understanding self-inductance.
The self-inductance of a solenoid is a property that measures its ability to induce a back emf in response to a change in current. It depends on factors such as the number of turns per unit length and the length of the solenoid.
Step 2: Explanation of options.
- (A) The current flowing through its medium: The current does not directly affect the self-inductance, although it influences the magnetic field.
- (B) The number of turns per unit length: The self-inductance of a solenoid increases with the number of turns per unit length. More turns result in a stronger magnetic field and higher inductance.
- (C) The length of the solenoid: The self-inductance of a solenoid is also affected by its length, as a longer solenoid has more space for the magnetic field to interact.
- (D) Both (B) and (C): The self-inductance of a solenoid depends on both the number of turns per unit length and the length of the solenoid.
Step 3: Conclusion.
The correct answer is (D) as the self-inductance of a solenoid depends on both the number of turns per unit length and its length.

Step 1: Understanding magnetic field in a solenoid.
A solenoid is a long wire wound in a cylindrical shape, and when current flows through it, it produces a magnetic field. The magnetic field lines inside the solenoid are parallel and uniform, aligning in the same direction as the axis of the solenoid. Step 2: Conclusion.
Thus, the direction of the magnetic field inside a current-carrying solenoid is parallel to its axis.