Magnet is a naturally occurring or artificially designed material which has a peculiar property of attracting some materials like iron, nickel and cobalt, called magnetic materials.
Magnets also have a directional property due to which a magnetic bar when suspended freely always stays in north-south direction. In this situation the end of the magnet which points towards geographical north is called north pole and the one which points towards south is called south pole. The two poles of a magnet are inseparable and like poles repel each other while unlike poles attract each other.
Electricity and magnetism were considered two separate phenomena, until, in 1820 Dutch Scientist HC Oersted found that when current is passed through a conductor a magnetic needle lying alongside shows a deflection. Thus. magnetism is now seen as a magnetic effect of electric current.
When direct current is passed through a cylindrical coil of wire (called solenoid), it behaves like a magnet. The strength of the electromagnet depends on: the number of turns per unit length in the coil, the strength of current and material of the core inside it. Electromagnets are used in many electrical devices like electric bell, telegraph, magnetic cranes.
A current carrying conductor placed in a magnetic field experiences a force. The direction of force is given by Fleming's Left Hand Rule, according to which if we stretch the fore finger, the central finger and the thumb of our left hand at right angles to each other and hold it in such a way that central finder points in the direction of current, fore finger in the direction of magnetic field, then the thumb will point in the direction of force.
A coil of wire when placed in a magnetic field experiences several forces due to which it tends to rotate. The tendency of rotation in the coil is measured in terms of a physical quantity called torque. Due to this torque the current carrying coil may be set into continuous rotatory motion. This is the principle of electric motor - the device which converts electrical energy into mechanical energy and is basic unit used in electric fans, irrigation pumps, etc.
Faraday discovered the phenomenon of electromagnetic induction, according to which a current is induced in a coil when the strength of magnetic field associated with the coil is changed. The current remains in the coil till the change in magnetic field is continued. Electromagnetic induction is the principle behind electric generators.
Depending on the way the energy is tapped out of a generator, the current output may be of two types: ac and dc. ac or alternating current reverses its direction periodically while dc or direct current is unidirectional.
Transformers are devices through which you can increase or decrease the level of ac voltage as required. When voltage is stepped up current is reduced in the same proportion and vice versa.
Fuse is a weak link in electric circuits, made of a wire of comparatively higher resistance and lower melting point (such as lead-tin alloy), used to protect the installation. If due to overloading, leakage, or short circuiting excessive current is to flow through the circuit the fuse blows off and saves the installation from the risks of this excessive current. These days, MCB is used in place of fuse.