Magnetic Effects of Electric Current
* When an electric current passes through a conductor, a magnetic field is created around the conductor. This phenomenon is known as the magnetic effect of electricity.
* A magnetic field is the extent of space surrounding a magnet where the magnet’s effect can be felt.
* Magnetic field lines represent the lines of action of the force acting on a unit north pole placed in a magnetic field.
* Maxwell’s right hand grip rule:
Holding a conductor in the right hand with the fingers curled around it and the thumb stretched out:
* The thumb denotes the direction of the current flow
* The direction of the curling of the fingers indicates the direction of the magnetic field lines.
* Maxwell’s corkscrew rule: On turning, if a right-handed corkscrew advances in the direction of current, then the direction of rotation of its head gives the direction of the magnetic field lines.
* A magnetic field caused by a current-carrying conductor consists of sets of concentric lines of force.
* The direction of the magnetic field lines depends on the direction of the current passed through the conductor.
* A solenoid consists of an insulated conducting wire wound on a cylindrical tube made of plastic or cardboard.
* An electromagnet is a magnet made up of a coil of insulated wire wrapped around a soft iron core that is magnetised only when current flows through the wire.
* Fleming’s left hand rule:
When the forefinger, middle finger and thumb of the left hand are stretched such that they are at the right angles to each other, then:
* The forefinger gives the direction of the magnetic field.
* The middle finger points in the direction of the current.
* The thumb gives the direction of the force acting on the current-carrying conductor placed in the external magnetic field.
* An electric motor converts electric energy into mechanical energy using the magnetic effect of electricity.
Electromagnetic Induction
* Electromagnetic induction (EMI) is the process of generating an electromotive force by moving a conductor through a magnetic field.
* The electromotive force generated due to electromagnetic induction is called induced emf.
* The current due to induced emf is called induced current.
* Michael Faraday hypothesised that current induced in a coil is due to a changing magnetic field.
Factors affecting EMI:
* Direction of movement of the magnet
* Orientation of the magnet
* Speed of movement of the magnet
* Strength of the magnet
* Cross sectional area of the conductor
* Faraday’s law states that the magnitude of induced emf, E, in any closed circuit is directly proportional to the rate of change of the magnetic flux, φ, through the circuit.
* Fleming’s right hand rule states that if the index finger points in the direction of the magnetic field and the thumb indicates the direction of the motion of the conductor, then the middle finger indicates the direction of the induced current flow in the conductor.
* An electric generator is used to convert mechanical energy into electrical energy, using electromagnetic induction.
* Alternating current (AC) is the current induced by an AC generator. AC current changes direction periodically.
* Direct current (DC) always flows in one direction, but its voltage may increase or decrease.
* Electrical components and wires fitted in a household to supply electricity to various appliances form a domestic electric circuit.
* Domestic electric circuits are connected to this network through main supply cables, commonly known as mains.
* The main supply cable has two wires. Live wire and neutral wire.
* Separate circuits may be used for power lines supplying 15 A and 5 A current.
* Domestic electric circuits also have earth wires to save users from severe electric shocks.
* An electric fuse is a safety device used to protect an electric circuit against excessive current