Heating Effect of electric current

Question 1 How heat is produced  when electric current is passed through a conductor?

Question 2 Define Joule’s law?

Question 3 How does electric heater,iron and water heater work on heating effect of current?

Question 4 Why does filament of an electric bulb is made up of tungsten?

Question 5 Why electric fuse in the electric circuit melts when large current flows in the circuit?

Question 6 Why does electric bulb glows when electric current flows through filament of the bulb?

Heating Effect of electric current

When electric current flows through a metallic conductor then heat is produced.

Metallic conductor has large number of electrons which move randomly.If a conductor is connected to source of electricity then free electrons move from negative terminal to positive terminal.They collide with atoms or ions of conductor and with each other.As a result of collision,kinetic energy of free electrons is transferred to atoms or ions.They then start vibrating with large amplitude.Thus total energy of ions increases.This increase in energy increases the temperature.Heat is produced when electric current flows through conductor.

     W

V=—–

      q
W=V * q

q=I*t

W=VIt

H=VIT

V=IR

H=I2RT

     V2T

H=——-

      R

The work done is equal to heat produced in the conductor.

Joule’s law can be stated as

The amount of heat produced in conductor is

1)Directly proportional to square of electric current flowing through it.

2)Directly proportional to resistance of conductor.

3)Directly proportional to time for which electric current flow through conductor.
Practical application of heating effect of current

1)Electric heater,iron,water heater work on heating effect of current.

When these appliances are connected to supply of electricity they become hot but wires remain cold.They are made of nichrome(high resistivity and hence high resistance).Heat produce is directly proportional to the resistance of material through which current flows.

Nichrome has high resistance so large amount of heat is produced and filament of appliance become hot.

Connecting wires are made up of Cu or Al with small resistance,so small heat is produced and they remain cold.
2)Electric bulb glows when electric current flows through filament of the bulb.

Filament of an electric bulb is made up of tungsten with high melting point.

Filament is enclosed in a glass envelop which is filled with nitrogen and argon gas.

Since resistance of thin filament is very high,so large heat is produced as electric current which flow through filament.Due to its large amount of heat produced,filament of bulb become white hot.Hence filament of bulb emits light and heat.
3)Electric fuse in the electric circuit melts when large current flows in the circuit

Electric fuse is a safety device connected in series with electric circuit.Electric fuse is a wire made up of material whose melting point is very low.(Cu or Sn alloy).

When large electric current flow through a circuit and hence through fuse wire,large amount of heat is produced.Due to this large heat,the fuse wire melts and circuit is broken so that current stop flowing in the circuit.This saves the electric circuit from burning.
Electric fuses are rated as 1A,2A,3A,5A,10A.

5A means maximum current that can flow through fuse wire.

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