Notes on Applications of Heating Effect of Electric Current
Heating effect of electric current has many useful applications in our daily life.
All the devices which work on heating effect of electric current or produce heat are based on Joule’s law of heating. Some of the devices which work on heating effect of electric current are:
Electric heater, electric iron, electric toaster, water heater electric fuse etc.
Principle of heating devices: All heating devices work on the principle of Joule’s heating effect. In them electric energy is converted into heat energy.
Electric bulb: In an electric bulb, the filament of bulb gives light because of heating effect
of electricity. The filament of bulb is generally made of tungsten metal; having melting point equal to 3380°C. The tungsten filament is coiled to give a very high resistance and is encased in a glass envelope. This glass envelope or bulb is filled with a low pressure inert gas such as nitrogen or argon to prolong the life of filament. When electricity passes through the coiled tungsten filament, it becomes hot and glows. The inert gas conducts the heat generated by the filament to the glass bulb from where the heat is radiated into the atmosphere.
Electric Heater
The primary component common to all electrical heaters is the electrical resistor.
When we turn a heater on, the electrical current that is produced heats up the thin, long coiled
nichrome wire components — better known as the heating coils. Since we know that alloys have more resistivity than their constituent metal, The nichrome wire being an alloy has high resistivity and low temperature coefficient of resistance. So electrical energy is turned into heat as the current passes through the nichrome wire(resistor). That’s why electric heaters are also known as resistance heating units.
However the connecting wire of heating devices does not become hot though it supplies electric current to heating devices.
Reason : Since connecting wire is made of low resistivity metals like copper or aluminium and allow electric current to pass through them easily therefore they do not become hot.
Notes on Applications of Heating Effect of Electric Current
Electric Fuse
It is a safety device which protect our appliances from damages when electric current passing through the circuit exceeds the safe limit.
Sometimes there can be a short circuit. More voltage and hence more current flows into the appliance than what it can handle. This can damage the electrical appliance and can even cause a fire.
Principle: Electric fuse also works on the principle of Joule’s heating effect of electric current.
How does it work: When electric current passing through the circuit exceeds the safe limit , fuse wire heats up and melts and thus breaks the circuit. Thus our appliances are saved from damage.
Generally a fuse wire of tin and lead alloy is used as a fuse wire. Copper and aluminium wire of proper area of cross-section and length is also used as fuse wire.
How is it connected : It is always connected in series in circuits.
A thin metallic wire or alloy wire of high resistance and low melting point is used as a fuse wire.
Notes on Applications of Heating Effect of Electric Current
Rating of Fuse
Fuses are generally rated at 1A, 2A, 3A, 5A and 10 A .
What does rating of fuse mean?: When a fuse has rating of 2A ,this means when magnitude of electric current passing through the circuit exceeds 2A , the fuse wire will heats up and melt and thus breaks the circuit.
How to calculate rating of fuse for a circuit or an appliance : let an electrical appliance consumes 2 Kw power at 220V , then the current required to run will be :
since P = VI 2000 = 220 × I
I = 2000/ 220
= 9.1 A
Here a fuse wire of rating 10 A must be used to protect the appliance.
If a fuse wire of rating 5 A is used , will it work?
No , because fuse wire of rating 5 A will heat up and melt.
Area of cross section and length of wire varies with rating of fuse. Since we know resistance of conductor depends upon area of cross section and length of conductor.
Notes on Applications of Heating Effect of Electric Current
Physics Formulae For Class 10
Light-Reflection and Refraction:- Chapter 10
Human Eye and The Colourful World:- Chapter 11
Magnetic Effects of Current:- Chapter 13
Sources of Energy:- Chapter 14