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Two AC questions

Consider in the first case, I have a ground potential sticked on a simple AC circuit, with a AC source and a linear resistor. However, when the polarity changes (say the current reverses its direction from going to the top of the circuit to going to the bottom of the circuit) Would all current sink to the ground instead of going around thru the resistor? So wouldn't such circuits be not making any senses?

In the second case, a common-emitter transistor circuit, the dc supply are connected to the AC source over the bottom of the diagram. Would the ac voltage, during a negative cycle, reinforce the dc supply in that transistor circuit?

Thanks Jack

Reply to
Jack
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Simple answer? No. All the current flowing through the resistor returns to the AC source, none of it flows to ground. The ground has no effect on the circulating current in either direction.

I don't understand what you mean. Are the AC and DC sources in series or parallel?

Try posting a schematic using

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Reply to
Andrew Holme

Does that mean the ac source (negative end during a negative cycle) has a lower resistance than the ground? I only know that the ground is a pond of charges with 0V potential. Do all electrons replenish from negative end of the ac source and charges never come from the ground?

/ | ------------ | |------| transistor ______ | cap \\ __ DC | | | AC | | |______________|__________________

Reply to
Jack

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Reply to
Jack

No.

Correct.

The not so simple answer is that the effect of the ground is vanishingly negligible, except in physically large circuits or at high RF frequencies.

The total voltage across the two sources in series is their sum. The AC component reinforces and opposes the DC voltage on alternate half cycles. If the DC voltage is 5V and the AC voltage is 1V peak, the sum varies between 4V and 6V.

BTW - That transistor would need some form of DC biasing in a practical circuit.

Reply to
Andrew Holme

Then I have a question. With ordinary circuit breakers (fuse) in an electric circuit, when the power surges/short-circuits , how come the electron can find its path quickly, grounding themselves, without delay? If nothing can "supersede" the path for the resistors? Thanks Jack

Reply to
Jack

At the instant the ground connection is attached, there may be a brief flow of charge, but this stops once the circuit node is anchored to 0V ground potential.

Reply to
Andrew Holme

Ummm Thanks... I would like to look into more of these topics. Any books recommended? Thanks Jack

Reply to
Jack

OK, so we're talking about the mains supply. There is a circuit breaker and a load resistor. The mains electricity system is physically large. It has capacitance to ground and is physically connected to ground at source.

Current flows to ground and the breaker trips if one side of the resistor is suddenly grounded. Ground current ceases once the load resistor reaches 0V ground potential. This may take a few microseconds, depending on the size of the circuit. Current will briefly continue to flow through the resistor also, but that too stops in microseconds.

Reply to
Andrew Holme

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