# The voltage and an electric heater

## Homework Statement

A 660[W] heater can work on 120[V]. if the voltage decreases to 110[V] what is the power that it consumes?

## Homework Equations

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

## 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]

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gneill
Mentor

Thanks, gneil

haruspex