Question

An immersion heater has a resistance of 20 ohms and is used with 240 V mains supply. What is its power output?

Answer 1

Let's find the current in immersion heater. According to Ohm's law:

$\displaystyle V = IR \; \; \Rightarrow \; \; I = \frac{V}{R}$

The power output is

$\displaystyle P = VI = \frac{V^2}{R} = \frac{240^2}{20}= 28\;800 \; \textrm{W} = 28.8 \; \textrm{kW}$

Answer: $28.8$ kW