State Joule's law of heating. Explain the workmg of electric filament bulb.
OR
State Ohm's law. How ammeter and voltmeter should be connected in electric circuit ? What is the use of these instruments, in the circuit ?

Explanation

Joule.s Law: When current of I ampere flows in a wire of resistance R `Omega` for t seconds, the heat energy dissipated by it is given by H = `I^(2)`Rt
(1) The filament of electric bulb must be made up of a substance so that it does not melt at very high temperature.
(2) Tungsten with high melting point of 3380" is used for making bulb filaments.
(3) The bulb is usually fiJJed with chemically inactive nitrogen and argon gases to prolong the life of filament.
(4) The filament gets extermely hot and emits light.
OR
• Ohm.s Law : It states that "Physical conditions remaining same, the current flowing through a conductor is directly proportional to the potential difference across its two ends". i.e., V `alpha` I
V = IR
• Where the constant of proportionality R is called the electrical resistance or resistance of the conductor.
• A voltmeter is connected in parallel with a device and an ammeter is connected in series.
• Voltmeter is used to measure the voltage while ammeter is used to measure the current flowing in the circuit.