Do heating elements have high or low resistances?

Discussion in 'Homework Help' started by mahela007, Sep 20, 2008.

  1. mahela007

    Thread Starter Active Member

    Jul 25, 2008
    45
    0
    Does the heating element in something like an electric hot water heater have high resistance or low resistance? I can't seem to find the answer the to that question. If it has low resistance , then why does the filament of a incandescent light bulb have high resistance?
     
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Heaters and lightbulbs have low resistance.

    For example , a 100W bulb. P = V^2/R

    R = V^2/P
    = 144 Ohms

    1000W heater
    R = 120^2/1000
    = 14.4 Ohms

    Keep in mind that this resistance is 'dynamic'. During startup, there is a much lower resistance seen. This is because as the filament heats, it's resistance increases. Therefore, the current goes down.

    Steve
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    I thought about that a bit more, and the answer is relative. Yes, the lightbulb's filament is high resistance in comparison to the wire used to connect it to the AC supply. But, it's certainly not high in comparison to a typical resistor used in an opamp circuit.

    Steve
     
  4. mahela007

    Thread Starter Active Member

    Jul 25, 2008
    45
    0
    could you pls tell me what an opamp circuit is?
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    how about a thank you for answering your original question?
     
  6. mahela007

    Thread Starter Active Member

    Jul 25, 2008
    45
    0
    hey... I dint mean that to be rude or anything... I really dont know what an opamp circuit is.. thanks anyway
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
  8. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
  9. DickCappels

    Moderator

    Aug 21, 2008
    2,654
    632
    "Does the heating element in something like an electric hot water heater have high resistance or low resistance?"

    Yes! Next question, please...

    More seriously:
    Hi or low compared to what?

    It will have the resistance required to dissipate the required power. It will be higher than the resistance of a penny but lower than the resistance of a 100 watt light bulb.
     
Loading...