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 resistanceof 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 energyneeded to raise the temperatureof the mug and the heater itself.
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 …
The power is given by the following expression P= U^2/R.