Physics
General Knowledge

Electric Power

Electric Power

The rate at which electrical energy is consumed in a circuit is called Electric Power. Its S.I. unit is watt.
» Kilowatt hour is the unit of energy and is equal to the energy consumed in the circuit at the rate of 1 kilowatt (1000 J/s) for 1 hour.
» 1 kilowatt hour = 3.6 x 106 joule.
» 1 kWh is also called board of trade unit.

Ammeter

Ammeter is a device used to measure electric current in a circuit. It is connected in series in the circuit.
» The resistance of an ideal ammeter is zero.

Voltmeter

Voltmeter is a device used to measure the potential difference between two point in a circuit. It is connected in parallel to the circuit.
» The resistance of an ideal voltmeter is infinite.

Electric fuse

Electric fuse is a protective used in series with an electric appliance to save it from being damaged due to high current. it is a small conducting wire of alloy of copper, tin and lead having low melting point.
» Pure fuse is made up of tin.

Galvanometer

Galvanometer is a device used to detect and electric current in a circuit. It can measure small electric current in a circuit. It can measure current up to 10-6 A.

Shunt : Shunt is a wire Of very small resistance.
» A galvanometer can be converted into an ammeter by connecting a shunt parallel to it.
» A galvanometer can be converted into a voltmeter by connecting a very high resistance in the series.

Electromagnetic induction

Whenever there is change of magnetic flux linked with a circuit, and emf is induced in the circuit. This phenomenon is called electro Magnetic Induction. The emf so develope is called induced emf and the current so generated (if circuit is closed) is called in called induced current.
Direction of induced current is determined with the help of Fleming’s right hand rule or Lenz law.

Transformer

Transformer is a device which converts low voltage A.C. into high voltage A.C. and high voltage A.C. into low voltage A.C. It is based on electromagnetic induction and can be used only in case of alternating current.

A.C. Dynamo (or generator): It is device used to convert mechanical energy into electrical energy. It works on the principle of electro-magnetic induction.

Electric motor : It is a device which converts electrical energy into mechanical energy.

Microphone

It converts sound energy into electrical energy and works on the principle of electromagnetic induction. In other words, microphone is an instrument for changing sound waves into electrical energy which may then be amplified transmitted or recorded.
» The current generated in the power stations are alternating current having voltage 22000 volt or more. In grid substations, with the help of transformer, their voltage is increased up to 132000 volt to minimise loss of energy in long distance transmission.