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 

#1
Dec1112, 09:00 PM

P: 37

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 150120(Edit: mA). Can someone tell me why???
Thank you. 



#2
Dec1112, 09:07 PM

Mentor
P: 7,291

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.
120150 whats? What kind of meter are you using? 



#3
Dec1112, 09:14 PM

Sci Advisor
PF Gold
P: 2,242

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 



#4
Dec1112, 09:16 PM

P: 37

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



#5
Dec1112, 09:18 PM

P: 37





#6
Dec1112, 09:19 PM

P: 53

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) 



#7
Dec1112, 09:21 PM

P: 37

The resistance of the 220 ohm resistor comes to about 218 ohm.




#8
Dec1112, 09:28 PM

P: 53

Can we verify the battery's voltage?




#9
Dec1112, 09:31 PM

Sci Advisor
PF Gold
P: 2,242

you still didnt tell us what sort of LED ?? Dave 



#10
Dec1112, 09:39 PM

Sci Advisor
P: 2,470

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? 



#11
Dec1112, 09:50 PM

P: 37

@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 



#12
Dec1112, 09:52 PM

P: 37





#13
Dec1112, 09:56 PM

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.




#14
Dec1112, 10:02 PM

P: 37

EDIT: Also the doubt I had is gone because I remeasured the current and it comes to about 41 mA. 



#15
Dec1112, 10:37 PM

Sci Advisor
PF Gold
P: 2,242

prob solved ....
the old saying ... a pic is worth 1000 words ;) Dave 


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