2.9 Applications of Heating Effect of Electric Current

The heating effect of electric current has wide range of applications in our daily life . Here we shall see a few common applications.

Electric Bulb

                      Have you ever tried to find how light is emitted from an electric bulb ? In an electric bulb actually a resistance wire is heated to very high temperature so that light of all wavelengths are emitted due to  incandescence. Can we make bulb filament using any metal? In order to get a high temperature the resistance of the filament must be high and also at high temperature the filament should not melt . Hence Filament material of a bulb should have high resistivity and high melting point. Power supply systems use constant voltage rather than current values .Hence the resistance of the bulb is inversely proportional to the power of bulb . Thus 100W bulb has lower resistance that 60W bulb.

Electric Fuse

                         Another unavoidable electric device used is electric fuse . Electric fuse is a device used to protect electric circuit from excess of current . The fuse wire material should have low melting point so that it melts off when the current exceeds the permissible value. Commonly used fuse wire material  is alloy of tin and lead. A fuse is basically a wire made up of a material having a suitable low resistivity and low melting point.

 Is there any importance to the length of the fuse wire ?

Note: The above question is quite natural but most of us neglect it. As length increase R increases and hence more heat is developed .But once the area increases the radiation loss also increases. Hence temperature due to current flow is independent of length.

    However if area is more R is lesser and surface area is more . Hence the temperature due to current flow decreases with increase in area of cross-section . Thus melting point will not be reached even though current exceeds permissible value. Hence area of cross section /thickness of  fuse wire  should have an optimum size depending on the permissible value of circuit current, while the length of fuse wire is immaterial.