Why resistor position matters? (Simple led project)

Hey take a look at the image below. Can anyone explain me why figure A does not work? I mean does not light the LED? The most logical is figure A to work and B not.

thanks :wink:

Hi xmarkx

Your diagram does not show which way round you have the LED in each circuit.

LEDs only conduct in one direction. It does not matter which side you put the resistor, but it DOES matter if you turned round the LED when changing the circuits.




Thank you for your answer @Hackscribble. I understood that was going wrong. I was not using a breadboard and I had the led and the resistor connected together. One way they were not working and I only thought that the resistor was the problem. But i was wrong. The problem was on the led. Thanks again.

I agree with hackscribble: I'll wager that to do the test you just picked the resistor / led up and turned it to simplyswitch the direction to the power, in which case the led is back to front in the one that doesn't work.

Lesson to learn here is to use the correct symbol for a diode which is --->|--- with a little squiggle to show an led's light. The "bar" end of the diode is the cathode.

EDIT... posted this in parallel to your own response above... crossed in mid-air