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The voltage and an electric heater

  • Thread starter Karol
  • Start date
  • #1
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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]
 

Answers and Replies

  • #2
gneill
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Your calculations look fine. The supposed answer is not correct.
 
  • #3
1,380
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Thanks, gneil
 
  • #4
haruspex
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My guess is the rated power should be given as 600W, not 660W.
 
  • #5
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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
 

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