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A heater coil has a resistance of 40 Ω and carries a current of 2.5 A…

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A heater coil has a resistance of $40\ \Omega$ and carries a current of $2.5\ \text{A}$ . How much heat does it produce in $15\ \text{s}$ ?

Need a reminder? The key ideaShow

Joule's law: $H = I^2 R t = VIt = \dfrac{V^2}{R}\,t$ . Power $P = VI = I^2 R = \dfrac{V^2}{R}$ , in watts. A fuse, in the live wire, melts when the current is too large.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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