The speed of flow of electrons is as low as 1 mm/s in a circuit. If the length of the wire from the battery to the bulb is 60mm, what is the time taken for the bulb to light up?

Instantaneous

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20s

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60s

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It never lights up

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Solution

The correct option is A Instantaneous
Current is established when the electrons start to move. When a potential difference is established, the speed at which current is established in the circuit is close to the speed of light. This is because, for current to be established in a circuit, the existence of a potential difference across the ends of the conductor is sufficient. It is not necessary that an electron at one end of the conductor must reach the other end.
For all practical purposes, the time taken to establish the current, once the potential difference is established, is instantaneous.

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Q. A 12-volt battery is connected to two light bulbs, as drawn in figure 1 light bulb 1 has resistance 3 ohms, while light bulb 2 has resistance 6 ohms. The battery has essentially no internal resistance, and all the wires are essentially resistanceless, too. When a light bulb is unscrewed, no current flows through that branch of the circuit. For instance, if light bulb 2 is unscrewed, current flows only around the lower loop of the circuit, which consist of the battery and light bulb 1. The more current flows through a light bulb, their equivalent resistance is

R_{e q} = R_{1} + R_{2}

. By contrast, when two reisistors are wired in parallel, their net resisance is given by

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Bulb 2 is now screwed in as a result, bulb 1 :

Current in a wire is due to the flow of electrons in the wire although the drift speed of the electron is very small yet an electric bulb lights up soon as it is switched on explain why

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