A refrigerator of 450 W works on a 230 V supply. Which fuse suits it: 3 A, 13 A or 30 A? Explain.

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A refrigerator of $450\ \text{W}$ works on a $230\ \text{V}$ supply. Which fuse suits it: $3\ \text{A}$ , $13\ \text{A}$ or $30\ \text{A}$ ? Explain.

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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