2. Once it has been established that the average drift speed of an electron is very, very slow, the question soon arises: Why does the light in a room or in a flashlight turn on immediately after the switched is turned on? Wouldn't there be a noticeable time delay before a charge carrier moves from the switch to the light bulb filament?

Current in a wire travels with a speed almost equal to speed of light. It is so because, when electron moves forward, it interacts with neighboring electrons. Due to this interaction, electric field gets disturbed. This flip or disturbance travels at a speed almost equal to speed of light. At the target it interacts with electron at the target. All through its path, it influences all the electrons on its path. We all know that electromagnetic wave consists of electric field which can influence electrons.

So current travels at speed of light.

According to the formula of current in terms of drift velocity,

I = n e A v

where, I is the current, n is the number of electrons per unit volume, e is the charge of an electron and v is the drift velocity of electrons

As the drift velocity is very small, but the number density of electrons is very large, so they collide very frequency and transfer energy. Thus, the light turns immediately.