Magnetic Effects of Electric Current — Important Questions

Uniform and parallel to the axis

Step 1: A solenoid is a coil of insulated wire wrapped in cylindrical form with many turns. Step 2: When current flows through the solenoid, each turn contributes to the magnetic field. Step 3: Inside the solenoid, all the field contributions add up constructively. Step 4: This results in a uniform magnetic field with field lines running parallel to the axis of the solenoid. Step 5: The uniform field inside makes solenoids useful for creating electromagnets and in many electrical devices.

Force on current-carrying conductor in magnetic field

Step 1: Fleming's left-hand rule determines the direction of force acting on a current-carrying conductor placed in a magnetic field. Step 2: Stretch your left hand with thumb, forefinger, and middle finger mutually perpendicular. Step 3: Point your forefinger in the direction of magnetic field. Step 4: Point your middle finger in the direction of current. Step 5: Your thumb will then point in the direction of force acting on the conductor. This rule is essential for understanding the working of electric motors.

Direction of force reverses

Step 1: The force on a current-carrying conductor in a magnetic field depends on both current direction and field direction. Step 2: According to Fleming's left-hand rule, when current direction changes, the middle finger points in opposite direction. Step 3: With forefinger (magnetic field) remaining the same, the thumb (force direction) must point in the opposite direction. Step 4: This reversal of force direction is demonstrated when we reverse battery connections in experiments. Step 5: The magnitude of force remains the same, only the direction changes, which is a fundamental principle us

Placing soft iron core inside a current-carrying solenoid

Step 1: An electromagnet requires both a magnetic field and a magnetizable material. Step 2: A solenoid carrying current creates a uniform magnetic field inside it. Step 3: When soft iron is placed inside this solenoid, it becomes magnetized due to the magnetic field. Step 4: Soft iron is preferred because it magnetizes easily and loses magnetism quickly when current stops. Step 5: This combination creates a temporary magnet that can be controlled by switching current on/off, making it useful in electric bells, cranes, and MRI machines.