Electromagnetism Short notes and Selected PYQs

Magnetic Effect: A current-carrying conductor produces a magnetic field around it.
Oersted's Experiment: Demonstrated that electric current produces magnetic field (deflects compass needle).
Right-Hand Thumb Rule: Thumb points in direction of current, curled fingers show direction of magnetic field.
Magnetic Field Lines: Concentric circles around straight conductor; direction given by right-hand rule.
Strength: Magnetic field strength increases with current and decreases with distance from conductor.

Solenoid: A coil of many circular turns of wire wound on a cylindrical core.
Magnetic Field Pattern: Similar to bar magnet with North and South poles at the ends.
Polarity: Determined by direction of current using right-hand grip rule.
Right-Hand Grip Rule: Fingers curl in direction of current, thumb points to North pole.
Strength: Field strength increases with number of turns and current; stronger inside the solenoid.

Electromagnet: A temporary magnet made by passing current through a solenoid with soft iron core.
Soft Iron Core: Enhances magnetic field due to high permeability and loses magnetism when current stops.
Strength: Depends on current, number of turns, and core material.
Advantages: Strength can be controlled, polarity can be reversed, can be switched on/off.
Applications: Electric bell, electric motors, magnetic cranes, relays, loudspeakers, MRI machines.

Fleming's Left-Hand Rule: Thumb = force (motion), First finger = magnetic field, Middle finger = current direction.
Force: F ∝ BIl, where B = magnetic field, I = current, l = length of conductor.
Direction: Perpendicular to both current and magnetic field.
Maximum Force: When conductor is perpendicular to magnetic field.
Zero Force: When conductor is parallel to magnetic field.

Principle: A current-carrying coil in magnetic field experiences a force and rotates.
Construction: Rectangular coil (armature), permanent magnet, split ring commutator, carbon brushes.
Function of Commutator: Reverses direction of current every half rotation to maintain continuous rotation.
Working: Force on opposite sides of coil causes rotation due to Fleming's left-hand rule.
Applications: Electric fans, washing machines, mixers, electric vehicles, industrial machinery.

Faraday's Discovery: Moving a magnet near a coil induces current in the coil.
Electromagnetic Induction: Production of electric current in a conductor due to changing magnetic field.
Fleming's Right-Hand Rule: Thumb = motion, First finger = field, Middle finger = induced current.
Factors: Induced current increases with speed of motion, strength of magnet, number of turns in coil.
Generator Principle: Converts mechanical energy to electrical energy using electromagnetic induction.
AC Generator: Produces alternating current using slip rings; DC generator uses split-ring commutator.

Electromagnetism