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# An immersion heater

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An immersion heater used to boil water for a single cup of tea plugs into a 120V outlet and is rated at 300W.

What is the resistance of the heater?

Suppose your super0sive, super-insulated tea mug contains 400g of water at a temp of 18 degrees Celsius. How long will this heater take to bring the water to a boil? Ignore the energy needed to raise the temperature of the mug and the heater itself.

##### Solution Summary

The power is given by the following expression P= U^2/R.

##### Solution Preview

The power is given by the following expression P= U^2/R, where U is a voltage and R is a resistance, solving for R you get:

R = U^2/P = 120^2/300 = 48 ...

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