Oersted's experiment, electromagnets, electromagnetic induction, electric motor, generator, and domestic wiring
Hans Christian Oersted discovered that a current-carrying conductor produces a magnetic field around it. When a compass is placed near a current-carrying wire, the needle deflects — proving the connection between electricity and magnetism.
Straight wire: Circular magnetic field lines around the wire
Direction given by Right-Hand Thumb Rule: Wrap right hand around wire with thumb pointing in direction of current — fingers point in direction of magnetic field.
Circular coil: Inside coil = nearly parallel field lines; centre acts like a bar magnet
Solenoid: Long coil of wire — produces strong, nearly uniform magnetic field inside (like a bar magnet)
Imagine gripping a wire with your right hand. Your thumb points in the direction of current flow. Your four fingers curl around the wire — they show the direction of magnetic field circles around the wire!
A solenoid with a soft iron core is called an electromagnet. When current flows, the solenoid magnetises the soft iron core, creating a strong magnet. When current stops, iron loses magnetism (temporary magnet).
Advantages: Can be switched on/off, strength adjustable by changing current/number of turns
Uses: Electric bells, cranes (lifting scrap iron), MRI machines, speakers, relays
Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular:
• Forefinger (First finger): Direction of Magnetic Field (B)
• Middle finger: Direction of Current (I)
• Thumb: Direction of Force (Motion) on conductor
Memory: FBI = Forefinger-B, Middle finger-I, Thumb = Motion
A device that converts electrical energy → mechanical (rotational) energy using the force on a current-carrying conductor in a magnetic field.
Components: Armature coil (rectangular, rotates) + Strong magnet + Split ring commutator + Carbon brushes
Working: Current in coil → force due to magnetic field → coil rotates → commutator reverses current every half rotation → continuous rotation in same direction.
Uses: Fans, refrigerators, washing machines, mixers, electric vehicles, pumps
When a conductor moves in a magnetic field (or magnetic field changes through a coil), an induced EMF and current are produced. This is Electromagnetic Induction.
This is the reverse of motor: mechanical energy → electrical energy
Stretch thumb, forefinger, middle finger of RIGHT hand mutually perpendicular:
• Forefinger: Direction of Magnetic Field
• Thumb: Direction of Motion of conductor
• Middle finger: Direction of Induced Current
AC Generator (Alternator): Uses slip rings → produces alternating current (direction reverses periodically). Used in power stations, alternators in cars.
DC Generator: Uses commutator → produces direct current (flows in one direction). Used in batteries, DC motors as generators.
In India: AC frequency = 50 Hz (current reverses 50 times per second)
Live wire (Red/Brown): 220V potential; carries current from supply
Neutral wire (Black/Blue): 0V potential; completes the circuit back to supply
Earth wire (Green/Yellow): Connected to earth; safety — carries fault current to ground
Potential difference between live and neutral = 220 V (AC in India)