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I'm very much a beginner experimenting for the first time with electronics, and I'm still trying to grasp the basics. On my breadboard, my LEDs have to be setup in a very specific way for them to work, the positive end being on the positive side and the negative node connecting to the negative side.

I thought the point was to get electricity to flow through the LED thus getting it to light up. Clearly electricity flows through my resistor even though it doesn't have a positive/negative node dichotomy. So why is it so for LEDS? Also if I may ask, what specifically causes one end to be negative and one end to be positive? What is the actual difference between the two nodes chemically?

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    \$\begingroup\$ I'm voting to close this question as off-topic because it can easily be answered with a little Googling. Lack of research. \$\endgroup\$ Dec 27, 2019 at 15:57
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    \$\begingroup\$ @LeonHeller I would cut him some slack. He is still at the point when he sees every component as a different kind of resistor. Obviously wrong but not uncommon. \$\endgroup\$
    – DKNguyen
    Dec 27, 2019 at 15:59
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    \$\begingroup\$ Have you heard of WIki? en.wikipedia.org/wiki/Light-emitting_diode \$\endgroup\$ Dec 27, 2019 at 16:01
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    \$\begingroup\$ @user3002540 Not "negatively and positively charged", but"polarized". \$\endgroup\$
    – DKNguyen
    Dec 27, 2019 at 16:11
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    \$\begingroup\$ This is a good example of a novice question where more experienced members can come across as rude. It's a perfectly valid question and it is worth having because it lacks "proper vocabulary" to help capture searches of other future visitors that also don't know the terminology. That said, it is always good practice to expend some time and effort researching topics before asking about them, and explain why your research was confusing or not helpful to you. \$\endgroup\$
    – JYelton
    Dec 27, 2019 at 16:35

2 Answers 2

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Different devices are different. It doesn't matter which end you hold to swing a stick, but it does matter if it is an axe or baseball bat. Whats the difference? Symmetry.

For a diode, one end of it is made of P doped silicon and the other end is N doped silicon. A resistor is just the same material throughout. If the component is not symmetrical then it stands to reason it won't behave symmetrically either.

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  • \$\begingroup\$ Sorry, I understand that it's different I guess I just didn't/don't understand why. I thought the current flows through which caused it to light up and I was just confused why the pins that connect to the breadboard couldn't be the same as the ones that connect a resistor. The phrasing I was using to search was poor, some of the answers here have given me a better idea of what to search. Thank you. \$\endgroup\$ Dec 27, 2019 at 16:13
  • \$\begingroup\$ @user3002540 LEDs are not incandescent lightbulbs. They work very differently. Incandescent lightbulbs are basically resistors. \$\endgroup\$
    – DKNguyen
    Dec 27, 2019 at 16:15
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    \$\begingroup\$ Semiconductor physics is a complex subject. If you want to understand the mechanics that give rise to polarity that's a course in electrical engineering, not a simple answer on stack exchange... \$\endgroup\$
    – vicatcu
    Dec 27, 2019 at 16:20
  • \$\begingroup\$ Yeah, the "why" for semiconductors turns out to be surprisingly hard to answer in a way that is both accurate and simple. \$\endgroup\$
    – pjc50
    Dec 27, 2019 at 17:09
  • \$\begingroup\$ @pjc50 "Why is the sky blue?" is a question that quickly devolves into similar level of physics as semiconductors. The only difference is that we have a much more direct experience and thus intuition of the sky's blueness so most people tend to be satisfied with answers that don't delve quite as deep. Similarly, few, if any, students ask "what is a force?" or "what is mass?" in an introductory mechanics class but will always ask "what is a line of flux?" in an intro electromagnetics class. Having an intuitive sense of things seems to make people more comfortable with less rigorous answers. \$\endgroup\$
    – DKNguyen
    Dec 27, 2019 at 18:11
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The "D" in LED stands for diode. Diodes allow current to flow in one direction but not the other. When (enough) current flows through the LED, it turns on.

In general, a diode is an p-n junction.

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  • \$\begingroup\$ Ok, I guess that's my confusion, that's just the construction of the diode itself. I think "one way current" is what I was looking for googling "why do diodes only allow one way current flow" seems to be closer to answering my question, I probably should have thought of that phrasing. Thanks for your help, I really appreciate it. \$\endgroup\$ Dec 27, 2019 at 16:11

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