Question

Though the same current flows through line wires or the filament of a bulb, yet only the latter glows.why?

Answer 1

HELLO THERE!

Thanks for such a logical and important question.

Here, let me tell you some points:

Line wires are wires that carry current from the power source to the load. These are made in such a way, and of such materials, which are excellent conductors of electricity, hence, whose resistance is low, so that loss of energy in form of heat is minimum (Loss of energy is given by the formula I²RT, where I is the current flowing, R is the resistance of the wire, and t is the time for which the current is flowing. If R is small, energy dissipated is small).

Hence, materials like copper and aluminium are used to make line wires, as they have very less resistivity (hence, good conductors).

Filament of a bulb is made up of such a material, which has a high resistivity, so that it offers a high resistance to the current flowing through it. Thus, huge amount of heat is formed in the wire (filament), and for this, it glows. Tungsten is used as a filament wire, because it has a high resistivity and high melting point (so that it does not melt at the high temperatures reached).

So, hope you got your answer, still, I'm summarising it again:

Line wires are made up of materials of low resistivity (good conductors), so when current flows through them, the heat formed is minimum, due to which they do not glow. On the other hand, a bulb filament is made up of such materials which have a high resistivity, so enough heat is formed in the wire to make it glow, when current flows through it. So, a line wire does not glow, but a filament glows, for the same amount of current.

HOPE MY ANSWER IS SATISFACTORY..

THANKS!