However at all times both voltage and current are present.

No.
At the instant the voltage is maximum the current is zero and vice versa.
For example, if you opened the circuit at the instant the current is zero, then the inductor current will stay at zero, and the capacitor will stay charged at the maximum voltage, but when the switch is again closed, the oscillations will continue exactly from were they were suspended.
(LTspice sim of this below):



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If you apply a voltage from a source with zero source resistance to a capacitor without a resistor in series with it, and the capacitor itself has no resistance, how long does it take for the voltage drop across the capacitor to be equal to the applied voltage? According to the equation t = R*C, the charging should be instantaneous, but that implies that the current went from a maximum to zero current also instantaneously which is impossible.

So what's your point as related to the subject of this thread?

 

My thought is that in charging/ discharging a reactive component (capacitor or inductor) there results at some point a maximum of voltage and a minimum of current and vice versa. However at all times both voltage and current are present.

If your applied signal is sinusoidal with no DC component, then both the voltage and the current do go to zero, although at different times.

If you apply a voltage from a source with zero source resistance to a capacitor without a resistor in series with it, and the capacitor itself has no resistance, how long does it take for the voltage drop across the capacitor to be equal to the applied voltage? According to the equation t = R*C, the charging should be instantaneous, but that implies that the current went from a maximum to zero current also instantaneously which is impossible.

Yes, under those ideal, on paper, conditions the current is an impulse of infinite magnitude and zero duration. Those conditions exist only on paper or in the mind. In the real world, there is always a limit to everything, if nothing else the limit at which things fail catastrophically.

 

No.
At the instant the voltage is maximum the current is zero and vice versa.
For example, if you opened the circuit at the instant the current is zero, then the inductor current will stay at zero, and the capacitor will stay charged at the maximum voltage, but when the switch is again closed, the oscillations will continue exactly from were they were suspended.
(LTspice sim of this below):

View attachment 363470

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So what's your point as related to the subject of this thread?

Without a voltage present, there can be no current. The thread starter I think maybe is seeing this as the problem in understanding current lag/ lead.

So in the case of the inductor after more than five time constants, the applied voltage is at zero, but the current in the inductor is sustained by the voltage of its electrical field. In the case of the capacitor, the voltage drop across the capacitor equals the applied voltage by virtue of the fact that the stored charge of the capacitor is nearly equal to that of the applied voltage. However there remains an infinitesimally small current flowing in the capacitor.

Edit: I take back my explanation of applying a DC voltage to an inductor. What really happens is that when first applying a DC voltage across a resistor in series with an inductor, the inductor has high reactance (something like resistance) to the applied voltage that causes all of the applied voltage to drop across the coil. After an electrical field has been established, then the reactance of the coil drops to zero volts and current through the inductor equals the applied voltage divided by the resistance of the resistor.

Voltage and current out of phase due to a capacitor or a coil in a circuit is due to energy storage and release.

 

Without a voltage present, there can be no current. The thread starter I think maybe is seeing this as the problem in understanding current lag/ lead.

So in the case of the inductor after more than five time constants, the applied voltage is at zero, but the current in the inductor is sustained by the voltage of its electrical field. In the case of the capacitor, the voltage drop across the capacitor equals the applied voltage by virtue of the fact that the stored charge of the capacitor is nearly equal to that of the applied voltage. However there remains an infinitesimally small current flowing in the capacitor.

Petehl you said ...

Without a voltage present, there can be no current.

While not my original question I agree with the above quote. Im not exactly keeping my head of water here but Im picking up dribes and drabs. In my ac world i couldnt understand why V and I dont stay in phase, magnitudes varying for sure i can understand that.

 

Without a voltage present, there can be no current.

Not true in all cases.
An ideal inductor (i.e. with a superconducting coil) will maintain a current indefinitely with no voltage applied or generated.
That's how an MRI machine maintains its large magnetic field.

 

I cannot for the life of me understand how voltage can lead current or current can lead voltage. Aren't they linked, don't they work in unison simultainiously. NM/culomb x culombs/sec = power. Is there a fluids example that might help me to see this.

What does NM stand for? You mean coulombs.

 

What does NM stand for? You mean coulombs.

NM might be newton-meters which would be units of force times distance. Newtons have units of mass times distance divided by time squared.

 

Without a voltage present, there can be no current. The thread starter I think maybe is seeing this as the problem in understanding current lag/ lead.

So in the case of the inductor after more than five time constants, the applied voltage is at zero, but the current in the inductor is sustained by the voltage of its electrical field. In the case of the capacitor, the voltage drop across the capacitor equals the applied voltage by virtue of the fact that the stored charge of the capacitor is nearly equal to that of the applied voltage. However there remains an infinitesimally small current flowing in the capacitor.

Edit: I take back my explanation of applying a DC voltage to an inductor. What really happens is that when first applying a DC voltage across a resistor in series with an inductor, the inductor has high reactance (something like resistance) to the applied voltage that causes all of the applied voltage to drop across the coil. After an electrical field has been established, then the reactance of the coil drops to zero volts and current through the inductor equals the applied voltage divided by the resistance of the resistor.

Voltage and current out of phase due to a capacitor or a coil in a circuit is due to energy storage and release.

There are too many inaccuracies in your post, starting with the first sentence. You need to review or delete your entire post.

What is the cause of infinitesimally small current flowing in the capacitor?

The reactance of the coil is constant. It never drops to zero,

 

What does NM stand for? You mean coulombs.

Newton meters

 

NM might be newton-meters which would be units of force times distance. Newtons have units of mass times distance divided by time squared.

I think a newton is a force no mass

 

What does NM stand for? You mean coulombs.

It should be Nm/C, better known as J/C, or joules/coulomb, which is even more widely known as V, or volts.

A Nm is a newton-meter, which is a unit of energy. Energy per unit charge is voltage, or electric potential.

 

Petehl you said ...

Without a voltage present, there can be no current.

While not my original question I agree with the above quote. Im not exactly keeping my head of water here but Im picking up dribes and drabs. In my ac world i couldnt understand why V and I dont stay in phase, magnitudes varying for sure i can understand that.

The claim that without a voltage present there can be no current is simply not the case, no matter how attractive it feels from an intuitive standpoint.

They don't stay in phase because of the defining physics of the devices. In a resistor, the instantaneous voltage is proportional to the instantaneous current. But, in an inductor, the instantaneous voltage is proportional not to the current at that moment, but to the rate at which the current is changing at the moment. Conversely, in a capacitor, the current is proportional to the rate at which the voltage is changing. Unlike a resistor, inductors and capacitors are energy storage devices, so these relationships are constrained by the mechanisms involved in storing energy in, or extracting it from, the device.

Also, keep in mind that "ELI the ICE man" refers to the phase relationship of voltage and current in a circuit that is in sinusoidal steady state operation. Take care not to read into it a more general interpretation than is there.

 

There are too many inaccuracies in your post, starting with the first sentence. You need to review or delete your entire post.

What is the cause of infinitesimally small current flowing in the capacitor?

The reactance of the coil is constant. It never drops to zero,

Except in rare cases, such as the lack of any resistance, there must be a voltage for their to be a current, isn't that correct? I did retract what I stated about an inductor in my post #23 which I would agree was very incorrect.

 

Except in rare cases, such as the lack of any resistance, there must be a voltage for their to be a current, isn't that correct? I did retract what I stated about an inductor in my post #23 which I would agree was very incorrect.

Not in the context of the TS's question, which is about instantaneous waveform values of voltage and current. If the voltage waveform crosses zero (i.e., changes sign), then it is (effectively) zero at some point between them. The current does not have to be zero at that same time. To see that this is the case, just consider a capacitor that starts at some positive voltage and is then discharged with a constant current until it eventually becomes charged at some negative voltage. There is a constant current during this entire time, but midway in the process the capacitor has reached zero charge and hence has zero voltage across it even though it still have a current flowing through it.

 

No.
At the instant the voltage is maximum the current is zero and vice versa.
For example, if you opened the circuit at the instant the current is zero, then the inductor current will stay at zero, and the capacitor will stay charged at the maximum voltage, but when the switch is again closed, the oscillations will continue exactly from were they were suspended.
(LTspice sim of this below):

View attachment 363470

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So what's your point as related to the subject of this thread?

Is V1 the voltage applied to L1 and C1? Is that voltage applied to both simultaneously? How is it that your circuit oscillates?

 

Is V1 the voltage applied to L1 and C1?

No.
The .ic V(1) command initializes node 1 (the capacitor) to 2V at the start of the sim, and the oscillation then proceeds by itself from that initial capacitive energy.
There is no voltage applied to the circuit during the oscillations.
V(1) is the voltage that occurs at the Node labeled "1" due to the circuit oscillation.

 

Except in rare cases, such as the lack of any resistance, there must be a voltage for their to be a current, isn't that correct? I did retract what I stated about an inductor in my post #23 which I would agree was very incorrect.

You are thinking of applied voltage in a resistive circuit. A pure LC circuit will oscillate indefinitely even after the applied voltage has been removed. Introduce resistance and the result is damped oscillation because energy is lost as heat in the resistor.

 

I think a newton is a force no mass

I never said that a newton was a mass. It is a force and by Newton's 2nd law it has units of mass times length divided by time squared.

 

You are thinking of applied voltage in a resistive circuit. A pure LC circuit will oscillate indefinitely even after the applied voltage has been removed. Introduce resistance and the result is damped oscillation because energy is lost as heat in the resistor.

View attachment 363533

In your circuit diagram you show voltage drops across all of the components in the circuit. It is those voltages that produce the current in the circuit when the battery voltage is removed. In the case of the coil, after the battery voltage source has been left connected to the circuit for a length of time allowing the circuit to arrive at a stable state, there actually would be no voltage drop across it but it then also has an electrical field.

Electrons in a conductor, doing nothing to the conductor, are moving randomly in the conductor. To obtain a current flow in one direction or the other, it is necessary for an electron motive force (EMF) or a voltage to be present. Isn't this what George Ohm discovered almost two centuries ago?

 

In your circuit diagram you show voltage drops across all of the components in the circuit. It is those voltages that produce the current in the circuit when the battery voltage is removed. In the case of the coil, after the battery voltage source has been left connected to the circuit for a length of time allowing the circuit to arrive at a stable state, there actually would be no voltage drop across it but it then also has an electrical field.

Electrons in a conductor, doing nothing to the conductor, are moving randomly in the conductor. To obtain a current flow in one direction or the other, it is necessary for an electron motive force (EMF) or a voltage to be present. Isn't this what George Ohm discovered almost two centuries ago?

No, that's not what he discovered. Ohm's Law is far from some universal law, it applies only to ohmic materials and devices, which are materials and devices that obey Ohm's Law. While that sounds circular, the important point is that there are many, many materials and devices that simply do not obey Ohm's Law. Capacitors and inductors are but just two of them.