Write the four factors affecting the resistance of a conductor.

The following four factors affect the electrical resistance of a conductor: (a) Temperature of the conductor: The resistance of all pure metal increases with an increase in temperature and on the other hand it, decreases by lowering the temperature. (b) Length of the conductor: The resistance of a conductor is directly proportional to its length. (c) Nature of the material of the conductor: When we take copper and aluminium wires of equal length and diameter, we will find that the resistance of the copper wire is less than the resistance of the aluminium wire. (d) Area of cross-section of the conductor or thickness of the conductor: The resistance of a conductor is inversely proportional to its area of cross-section.

Define the Electric fuse.

An electric fuse is a device that limits the current in an electric circuit so that it easily melts due to overheating when excessive current passes through it. The fuse wire is connected in series, in an electric circuit. When a large amount of current passes through the circuit, the fuse wire melts due to Joule’s heating effect and hence the circuit gets disconnected. Hence, the circuit and the electric appliances are saved from any damage. The fuse wire is made up of a material whose melting point is relatively low. A fuse wire is made up of a wire of an alloy of 75 % lead and 25 % tin which melts at 200 ° C . In the household circuit, a fuse is always connected in live wire. The fuse used in an electrical appliance consists of a glass tube having a thin fuse wire sealed inside it.

Write the SI unit of Electric Charge.

An electric charge can be defined as a physical property of a matter or substance that causes it to experience a force when placed near to other electrically charged matter or substance. The SI unit of electric charge is coulomb and is represented as ‘ C ’ . 1 coulomb is that quantity of electric charge which exerts a force of 9 × 10 9 N on an equal charge placed at a distance of 1 m from it.

Define electric current and write its S.l. unit.

The amount of charge, flowing through any cross-section of a conductor in unit time is known as electric current. In other words, electric current may be defined as the rate of flow of electric charge per unit time. Electric current = charge time The SI unit of current is ampere named after a French scientist, Andre Marie Ampere. It is denoted by ‘ A ’ .

A German physicist, George Simon Ohm established the relation between the potential difference and current, which is known as Ohm’s Law. Ohm's law states that at constant temperature the current flowing through a conductor is directly proportional to the potential difference across its ends.