NCERT Class 10 The most Important Basic concepts of chapter 13 (part 2)

The most Important points of Magnetic Effects of Electric Current (part-2)

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21. Electromagnetic induction: Whenever the Magnetic lines of force passing through a closed circuit change, a voltage and hence a current is induced in it. This phenomenon is called electromagnetic induction. It was discovered by Michael Faraday in 1831.

22. Fleming's right-hand rule: This rule gives the direction of induced current in a conductor. According to this rule if we hold the thumb, the forefinger and the central finger of the right hand mutually perpendicular to each other and if the forefinger points in the direction of the Magnetic field, the thumb in the direction of motion of the conductor, then the central finger points in the direction of the induced current in the conductor.

23. Electric generator or a dynamo: It is a device to convert mechanical energy into electric energy. It is based on the principle of electromagnetic induction that a current is induced in a closed circuit when the Magnetic field passing through it changes. 

24. Direct current: It is that current which flows in a circuit with a constant magnitude in the same direction.

25. Alternating current: It is that current whose magnitude and direction change alternately and regularly with the passage of time. 

26. Domestic wiring: The electricity from the mains is supplied to the houses using a three-core wiring called The Live , The Neutral and The Earth. The live wire is red in colour and brings in the current. The black neutral wire is the return wire. The green Earth wire is connected to a metal plate deep in the earth. It is a safety measure and does not affect the supply in any way.

27. Electric fuse: It is a safety device to protect an electric circuit from overloading or short circuiting. It is a piece of wire of a material of low melting point which is connected to the live wire in the circuit. When an excessive current flows, the fuse melts and the circuit is broken. Fuse wire is made of pure tin or tin-copper alloy.

28. Earthing: Earthing of an electrical appliance means connecting the metallic body of the powdered appliance to the earth through the earth wire. It is a safety measure which ensures any leakage of current to the metallic body of the appliance keeps its potential equal to that of the earth (zero volt) and the user may not get a severe electric shock.

29. Overloading: If the current drawn from the mains exceeds the safety limit (5A for domestic line and 15 A for power line), then this is known as overloading. A circuit can be protected from overloading by using an electric fuse. 

30. Short circuiting: If due to defective or damage wiring, the live and neutral wires come in direct contact, the resistance of the circuit becomes almost zero and an extremely large current flows through the circuit. This is called short circuiting. Appliances can be protected from short circuiting by using an electric fuse in live wire.