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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