1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculate percentage change in heat output

  1. May 11, 2012 #1
    1. The problem statement, all variables and given/known data
    A 500W heating unit is designed to operate on a 115V line. If the line voltage drops to 110V, calculate the percentage drop in heat output.

    2. Relevant equations

    3. The attempt at a solution

    Use V=115, then use V=110, use Power P=500...but not sure how

    p.s. I am a UK Physics student. I was wondering could you also say whether you are in the UK or US or....
    Last edited: May 11, 2012
  2. jcsd
  3. May 11, 2012 #2
    Find the resistance of the heater. Use that value of resistance and 110 volts to find new power output. %=(initial-finial)*100/initial
  4. May 11, 2012 #3
    Thanks thats great! I've done it now
  5. May 11, 2012 #4
    I got an answer of 8.5%! sounds right....

    Btw what do people think about the questions on online-exam-solutions?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook