Chapter 18, Problem 14Q

To determine

To explain:

When a light bulb of a reading lamp is driven by alternating current, the same electrons pass again and again to the bulb’s filament. Explain how the bulb keeps on emitting light and does not stop burning out after the first pass of electrons through it.

Answer to Problem 14Q

Solution:

It happens because it is not the ‘same’ or ‘different’ electrons which are responsible for burning out of bulbs but their energy.

Explanation of Solution

Yes, it is correct that when a reading lamp is driven by ac power, the same electrons pass through the filament of the lamp over and over again because the alternating current, keeps on changing its direction of flow from one side to another. But the lamp, emitting light, has nothing to do with the issue whether the ‘same’ electrons are entering into the lamp or ‘different’.

The thing is that when the electrons enter into the resistive environment of the electric bulb, forcefully, the resistance of the light bulb works as a dissipative force to the incoming electrons and the energy of the electrons keep on dissipating inside the light-bulb, whether the ‘same’ electrons enter into the lamp or ‘different’. As, we know that energy can neither be created nor be destroyed, so this dissipated energy is converted into the light energy and we say that the light-bulb is burning out.