# 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

Apr 5, 2008
19,792
4,105

Nov 17, 2003
6,960
171
9. ### DickCappels Moderator

Aug 21, 2008
5,668
1,778
"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.