71 votes

Why are two wires used in railway overhead equipment?

Overhead line worker here. It's about speed. To answer your question, the purpose of the catenary wire is to get the contact wire to lay flat, so it isn't catenary itself. In your second photo, there ...
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12 votes

Why are two wires used in railway overhead equipment?

It isn't to do with current-carrying capacity; it is to maintain good contact between the current-carrying wire and the pantograph pickup on the locomotive, as it allows the contact wire to be ...
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  • 341
6 votes
Accepted

How friction between stator and rotor is dealt with in an electric engine/motor

... there's no space between the rotor and the stator. There is always an air gap between the rotor and stator. Iron has a permeability of about 1000 times that of air so the trick for maximum ...
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  • 7,479
6 votes

Why are two wires used in railway overhead equipment?

Why two wires: A wire hanged at two points sags (it forms a "catenary curve"). The pantograph can only handle a certain sag before losing contact and arcing. The acceptable sag depends on ...
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  • 231
2 votes
Accepted

Find the values of resistance R and inductance L in the R-L-C circuit

Yes. Since the phase of the voltage is not explicitly mentioned, it can be assumed that it is the reference and hence aligned to the OX axis. The current phase is specified in the question. The ...
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  • 581
2 votes

How do 120V AC dimmable LED bulbs advertised as "flicker free" work?

Flicker can be minimized by choosing a phosphor in the design of the full-spectrum white LED that has a long persistence time. When you turn off one of these LED arrays, you can see that the light ...
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2 votes

Would the below thermal generator work properly and provide surplus energy?

Could it work? Yes. Is it practical for any scale? No. As @DKNguyen says in their comment, if you had a free source of these components you could generate this heat and use it to do things. But it ...
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  • 4,374
2 votes

Is half of depletion region a part of N region or P region?

Not true. The depletion region width depends on the doping. You can think that the non-moving +charge ("the bound charge") in the depleted N side has as much charge as the depleted area in ...
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1 vote
Accepted

What is this component on the face of an analog clock?

That is a light-dependent resistor, commonly made of cadmium sulfide. When light shines on it, its resistance goes down by a significant amount, and as such these devices found use in film cameras to ...
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1 vote

Measurement of actual carbon dioxide mass emitted from a diesel engine

Pull off a sample of the exhaust gas of known volume and bubble it through a calcium hydroxide solution, to convert all the CO2 to CaCO3. filter, dry, and weigh the CaCO3. knowing how much CO2 was in ...
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