# The voltage and an electric heater

1. Dec 27, 2014

### Karol

1. The problem statement, all variables and given/known data
A 660[W] heater can work on 120[V]. if the voltage decreases to 110[V] what is the power that it consumes?

2. Relevant equations
$$V=iR$$
$$P=iV$$
For pure resistance: $P=i^2R$

3. The attempt at a solution
The current at 660[W]: $P=i\cdot 120\rightarrow i=5.5[A]$
The resistance: $660=5.5^2\cdot R\rightarrow R=22[\Omega]$
The new current: $V=iR\rightarrow 110=i\cdot 22\rightarrow i=5[A]$
The new power consumption: $P=i\cdot V=5\cdot 110=550[W]$
And with another method: $P=i^2\cdot R=5^2\cdot 22=550[W]$
It is written that it should be 500[W]

2. Dec 27, 2014

### Staff: Mentor

3. Dec 27, 2014

### Karol

Thanks, gneil

4. Dec 27, 2014

### haruspex

My guess is the rated power should be given as 600W, not 660W.

5. Dec 28, 2014

### Karol

Thank you too, haruspex, but the other partial answers to this question, which i didn't fully copy here, fit 660[W], but i guess this problem is solved