I have been taught right from highschool that a conductor can charge through conduction, induction and friction. Yet a lot of physicists challenge me that a conductor cannot store charge? Who's right and who's wrong?
Electrical – Can a conductor store charge
physics
Related Solutions
Well, what happens if you try to remove an enormous amount of electrons from the wire? You'll leave behind the positive metal ions, so the wire will become charged positive. This pulls strongly on the electrons you're trying to remove.
The same thing happens with just one electron. It will be attracted to the wire by the positive charge left behind. And this attraction is much stronger when the electron is close to the wire surface.
Details: pull an electron a little way outside the metal surface. Now this individual un-canceled electron can repel the mobile electrons in the wire, leaving positive charges exposed. The positive charges attract the removed electron. But if we pull the electron farther away, the patch of positive charges becomes wider and overall weaker. The attraction is strong when the electron is first removed, and less when it's pulled farther from the metal surface. There's a physics rule-of-thumb to cover this: the positive charge in the metal behaves just like a single negative electron, and it acts like a mirror-image of the electron being removed. (Look up "image charge.")
And what the book probably discusses later is... hot filaments. If the wire is white hot, some of the mobile electrons are zooming around fast enough that they can fly a large distance away from the wire before being pulled back. The hot filament in a light bulb or vacuum tube is surrounded by an electron cloud.
There's green and then there's other green. This is why in engineering we use numbers instead of vague words. It is best to specify the actual wavelength.
Most common "green" LEDs are on the yellow end of what most people consider green. These do have about 2.1 V drop at reasonable currents. This type is the cheap and common "green" variety. This wavelength of green corresponds well to the peak sensitivity of our eyes.
There are other "green" LEDs that use different semiconductor substances and are more toward the bluish end of what most people would call green. These of course have a higher forward drop due to the physics you seem to understand correctly. These are much less common and typically more expensive. Their lumen specs also don't look as good, in part because this wavelength is a bit shorter than the peak sensitivity of human eyes.
My guess is that your professor deliberately gave you the unusual green type of LED to make you think a bit, learn not to take things for granted, and impress on you the need for real numbers as opposed to vague words like "green".
Best Answer
When analyzing circuits with resistors, inductors, capacitors, transistors, diodes batteries, etc connected together by conductors, you should assume that none of these circuit elements can or do store any charges. If you think charges can go into one side of a conductor without an equal number of charges exiting the other side of the conductor, you will find yourself very confused and unable to analyze any circuits or have any kind of intuitive feel for how circuits work.
In real life, any object which is surrounded by a dielectric can possibly acquire a net charge (by various methods), and therefore experience electrostatic attraction or repulsion, but charge storage is not an important concept in circuit analysis.
Please note that we sometimes say that capacitors or batteries "store charge," but this is not true in the sense you are asking about. Every time a mobile charge flows into one terminal of a capacitor or battery, another one flows out the other terminal. For any circuit element with two terminals, the current flowing in is equal in magnitude to the current flowing out instantaneously at all times.
Otherwise, we would not be able to use KCL to analyze circuits.