Doubting Ohm's Law: LED & 220Ω Resistor

In summary: LED and 220Ω resistor in series with a 9v battery should be no more than 41mA according to Ohm's law. However, the multimeter readings were consistently between 120-150 mA. The circuit diagram and details of the setup were requested for further assistance. The issue was later resolved by realizing that the resistor was shorted out due to its placement on the breadboard and the current was re-measured to be around 41 mA.
  • #1
anj16
38
0
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.
 
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  • #2


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?
 
  • #3


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


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

Integral said:
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.
 
  • #5


davenn said:
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?
 
  • #6


anj16 said:
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)
 
  • #7


The resistance of the 220 ohm resistor comes to about 218 ohm.
 
  • #8


Can we verify the battery's voltage?
 
  • #9


anj16 said:
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
 
  • #10


davenn said:
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?
 
  • #11


@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
 

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  • #12


BackEMF said:
Can we verify the battery's voltage?

The voltage of the battery is 9v
 
  • #13


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


K^2 said:
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.
 
  • #15


prob solved ...

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

Dave
 
  • #16


K^2 said:
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.

yup fair comment :)

D
 

1. What is Ohm's Law?

Ohm's Law is a fundamental principle in physics that states the relationship between voltage, current, and resistance in an electrical circuit. It states that the current flowing through a conductor is directly proportional to the voltage applied and inversely proportional to the resistance of the conductor.

2. How does Ohm's Law apply to LEDs and 220Ω resistors?

In the case of LEDs and 220Ω resistors, Ohm's Law can be used to determine the appropriate resistor value needed to ensure the LED receives the correct amount of current. The voltage drop across an LED is typically around 2-3 volts, so by using Ohm's Law (V=IR), we can calculate the necessary resistance to limit the current to a safe level for the LED.

3. Why do some people doubt Ohm's Law when it comes to LEDs and 220Ω resistors?

Some people may doubt Ohm's Law in this context because LEDs have a non-linear relationship between voltage and current. This means that as the voltage increases, the current does not increase at a constant rate, which can lead to unexpected results when using Ohm's Law to calculate the necessary resistor value.

4. How can I confirm or test Ohm's Law when using LEDs and 220Ω resistors?

One way to confirm Ohm's Law in this scenario is to measure the voltage and current in the circuit using a multimeter. By adjusting the voltage and resistance, you can see how changes in one variable affect the others, thus confirming the principles of Ohm's Law.

5. Are there any other factors besides Ohm's Law that can affect the operation of LEDs and 220Ω resistors?

Yes, there are other factors that can affect the operation of LEDs and resistors, such as temperature and manufacturing variations. These can cause slight deviations from the expected results when using Ohm's Law, so it is important to consider these factors when designing a circuit.

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