# I am starting to doubt Ohm's law. I would like someone to point out why I am wrong.

by anj16
Tags: ohm's law
 P: 38 As the title states I am really doubting Ohm's law. This is why: On a breadboard I placed a white LED and a 220Ω resistor with the 9v battery all in series. The total current flowing through the circuit shouldn't be more than 41mA by V=IR, but my multimeter points between the range of 150-120(Edit: mA). Can someone tell me why??? Thank you.
 Emeritus Sci Advisor PF Gold P: 7,337 We can't help without knowing what you are doing. A circiut diagram including how the meter is connected would help. Try to diagram what you have on the breadboard. 120-150 whats? What kind of meter are you using?
 Sci Advisor PF Gold P: 2,741 what sort of white LED is it give us a part number ? it may be one that draws more current Hint.... If you ever want to doubt a known physical law, assume it's something you are doing wrong, not the law ;) Dave
P: 38
I am starting to doubt Ohm's law. I would like someone to point out why I am wrong.

 Quote by Integral 120-150 whats? What kind of meter are you using?
Sorry about that I have edited it in the original post.

 Quote by Integral We can't help without knowing what you are doing. A circiut diagram including how the meter is connected would help. Try to diagram what you have on the breadboard.
Just so you know the correct way of connecting a meter in a circuit to measure the current is to connect it in series. which I did.
P: 38
 Quote by davenn what sort of white LED is it give us a part number ? it may be one that draws more current Hint.... If you ever want to doubt a known physical law, assume it's something you are doing wrong, not the law ;) Dave
I agree with you which is why I thought someone could point out where I am wrong. And about drawing more current wouldn't the current be restricted by the resistor?
P: 53
 Quote by anj16 As the title states I am really doubting Ohm's law. This is why: On a breadboard I placed a white LED and a 220Ω resistor with the 9v battery all in series. The total current flowing through the circuit shouldn't be more than 41mA by V=IR, but my multimeter points between the range of 150-120(Edit: mA). Can someone tell me why??? Thank you.
1) Measure the actual resistance of the "220 ohm" resistor.
2) Check the accuracy of the meter (use another meter - digital might be better as it would probably change the circuit less than and analgoue one)
 P: 38 The resistance of the 220 ohm resistor comes to about 218 ohm.
 P: 53 Can we verify the battery's voltage?
PF Gold
P: 2,741
 Quote by anj16 I agree with you which is why I thought someone could point out where I am wrong. And about drawing more current wouldn't the current be restricted by the resistor?
yes, but the calculated total current through the circuit is a combination of the total resistance of the resistor and of the forward resistance of the LED

you still didnt tell us what sort of LED ??

Dave
P: 2,470
 Quote by davenn yes, but the calculated total current through the circuit is a combination of the total resistance of the resistor and of the forward resistance of the LED
Unless LED develops a negative voltage drop, that seems kind of irrelevant, no? 9V / 220 Ohm = 41mA.

Any LED will actually reduce voltage by about 1 - 2 volts. So the current with an LED should be even less than 41mA. 150+ mA cannot be explained by any kind of LED.

anj16, can you take a picture of your setup?
 P: 38 @Dave about the part# for the LED, I have no clue. I bought in bulk off Ebay. I have attached a picture of the setup Attached Thumbnails
P: 38
 Quote by BackEMF Can we verify the battery's voltage?
The voltage of the battery is 9v
 Sci Advisor P: 2,470 Isn't the entire + line connected on the breadboard? If so, your resistor is shorted out. Try checking resistance while it is in the breadboard.
P: 38
 Quote by K^2 Isn't the entire + line connected on the breadboard? If so, your resistor is shorted out. Try checking resistance while it is in the breadboard.
Thank you so much!! I never thought about that. I think I need a break from this ;)

EDIT: Also the doubt I had is gone because I re-measured the current and it comes to about 41 mA.
 Sci Advisor PF Gold P: 2,741 prob solved .... the old saying ... a pic is worth 1000 words ;) Dave