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Question

What will be the power delivered by a lamp that uses 120 joules of energy in 2 minutes?

The correct answer is

1 watt

Power is the rate at which energy is used or work is done: \(P = \frac{E}{t}\), where energy is in joules and time is in seconds, giving power in watts.

Time \(t = 2\text{ min} = 2 \times 60 = 120\text{ s}\), and energy \(E = 120\text{ J}\).

So \(P = \frac{120\text{ J}}{120\text{ s}} = 1\text{ W}\).

Check: a lamp of power 1 W uses 1 joule every second, so in 120 seconds it uses \(1 \times 120 = 120\text{ J}\), which matches the energy given.

Hence, 1 watt.

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