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It is possible for a capacitor to have a net charge. However, most components have a small capacitance with respect to infinity. Unless you're dealing with a huge metal ball, it will take a large voltage in order to get any appreciable charge there.

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Light is emitted from a p-n junction for the same reason it is emitted in any other atomic process: because of an oscillating charge distribution. During the finite time the electron spends crossing the gap, it is in a superposition of two states: the low-energy (low frequency) and high energy (high frequency) states. The charge density is calculated by ...

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Generally speaking the electron and the atom, when separated, are in a state with greater energy respect to the situation in witch are bounded. They will tend to minimize their total energy thus expelling "something" containing this energy difference. In the case of direct gap semiconductors (as in LEDS) this "something" should contain a lot of energy and ...

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You said it yourself : electron-hole recombination lowers the energy of the system ; by conservation of energy, energy must be emitted somehow. Think of the electron and the hole as quasiparticles of the system with a certain energy. When they recombine this energy is transferred to a photon.

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A capacitor can contain a certain amount of charge for a given voltage: $$Q = CV$$ When you have more than one capacitor in parallel, they have the same voltage (because they are in parallel), and each stores a certain charge. The total charge (at a given voltage) will be the sum of the charges on all the capacitors. Now if you have a certain load (for ...

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Yes, oscilloscopes will eventually wear out. They last a long time, if they are taken care of. There are many vintage scopes out there that are 30+ years old that still work perfectly. Here are a few examples of failure modes. There are probably more. 1.) Phosphor coating on the inside of the tube wears out, causing the display to dim. 2.) The tube develops ...

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No! Any slab, however flat, will have roughness much larger than the inter-atomic crystal spacing and hence continuous contact at the atomic level will not be possible. The junction will behave as a discontinuity for the flowing charge carriers. On adding precisely a small quantity of pentavelent impurity, in a thin p-type semiconductor wafer, part of the ...

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