Two AC questions

[Jack]

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

 

[Andrew Holme]

"Jack" <jl@knight.com> wrote in message news:47daf762@127.0.0.1...

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?

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.

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?

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

Try posting a schematic using http://www.tech-chat.de/aacircuit.html

 

[Jack]

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?

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.

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?

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?

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

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

Try posting a schematic using http://www.tech-chat.de/aacircuit.html

 

[Jack]

"Jack" <jl@knight.com> źśźgŠóślĽóˇsťD:47db1a66$1@127.0.0.1...

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?

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.

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?


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?

I don't understand what you mean. Are the AC and DC sources in series or
parallel?
/ |
------------ | |------| transistor ______
| cap \ __ DC
| | |
AC | |
|______________|__________________

Sorry my IE7 just gone crook....

Try posting a schematic using http://www.tech-chat.de/aacircuit.html

 

[Andrew Holme]

"Jack" <jl@knight.com> wrote in message news:47db1a66$1@127.0.0.1...

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?

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.

Does that mean the ac source (negative end during a negative cycle) has a
lower resistance than the ground?

No.

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?

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.

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?

I don't understand what you mean. Are the AC and DC sources in series or
parallel?
/ |
------------ | |------| transistor ______
| cap \ __ DC
| | |
AC | |
|______________|__________________

Try posting a schematic using http://www.tech-chat.de/aacircuit.html

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.

 

[Jack]

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?

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.

Does that mean the ac source (negative end during a negative cycle) has a
lower resistance than the ground?

No.

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?

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.

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

 

[Andrew Holme]

"Andrew Holme" <ah@nospam.co.uk> wrote in message
news:frf7p7$rts$1$8300dec7@news.demon.co.uk...

"Jack" <jl@knight.com> wrote in message news:47db1a66$1@127.0.0.1...
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?

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.

Does that mean the ac source (negative end during a negative cycle) has a
lower resistance than the ground?

No.

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?

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.

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.

 

[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.

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

 

[Andrew Holme]

"Jack" <jl@knight.com> wrote in message news:47db26d3$1@127.0.0.1...

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?

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.

Does that mean the ac source (negative end during a negative cycle) has
a lower resistance than the ground?

No.

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?

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.

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

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.

 

On 3ÔÂ15ČŐ, ÉĎÎç6Ęą08ˇÖ, "Jack" <j...@knight.com> wrote:

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

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