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Why capacitor oppose change in voltage and allows current to flow?
Wiki User
∙ 11y ago
Because that is what a capacitor does, resist a change in voltage. It holds a certain amount of energy per charge (voltage), and to change that voltage requires current proportionally to the capacitance.
Wiki User
∙ 13y ago
Wiki User
∙ 14y agoWhen the capacitor is completely charged, and sudden variations occur, the capacitor opposes variations by discharging itself and providing same voltage at output.
Wiki User
∙ 11y agoan electric field induced/generates in capacitor plates so it oppose incoming voltages... so voltage is opposed.. not the current...
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What is the value of capacitor voltage and current after 5 time constant?
After 5 time constants, capacitor voltage/current will be about 99.3% of the input step change.
How could a capacitor have voltage but no current?
Voltage and current are two different things. Voltage is potential energy per charge, in joules per coulomb, while current is charge transfer rate, in coulombs per second. Its that same as saying that a battery has voltage but no current, because there is no load. Well, a capacitor resists a change in voltage by requiring a current to change the voltage. Once that voltage is achieved, there is infinite resistance to the voltage, and thus no current.
Why does the current lead the voltage across a capacitor by 90 degree rather than lag it?
A: Because a capacitor have to have time to charge to the voltage In a capacitor, the current depends on the voltage difference across it. On AC, this makes it charge, if the voltage is increasing above zero, and discharge if the voltage is reducing towards zero. Because a capacitor has almost no internal resistance, and most loads that it is connected to have only very small resistances in series with the capacitor, the charging and discharging currents depend pretty much on the rate at which the voltage is changing. At the zero crossing point of the sine-wave, when the voltage is actually zero, the rate of change of voltage is very high (the sine-wave is at its steepest), so the current is also very high. If the voltage is positive-going, the current is positive, and if the voltage is negative-going, the current is negative. At the peak of the voltage waveform, the rate of change of voltage is zero or very low (the sine-wave is flat, and not really changing its voltage) so the current is zero, too. Since the maximum positive current occurs when the voltage is passing through zero, going positive, and the maximum negative current happens when the voltage is passing through zero, going negative, the current peaks happen 90 degrees before the voltage peaks, so the current is said to lead the voltage. This is the same as saying the voltage lags the current by 90 degrees.
What is the reason behind the lag of current in inductor lead in capacitor?
The physics of the energy storage. In an inductor, the current must fight against the stored energy in the magnetic field which tries to keep the current unchanged. Any change in the current lags the voltage since the stored energy impacts the adjustment. Similarly, the "displacement" current in a capacitor leads the electric field buildup in a capacitor, causing the voltage to lag the current until the stored energy building up in the electric field stabilizes. Any change in the voltage is first preceded by a change in the displacement current.
Capacitance is the property of an electrical circuit that?
A capacitor resists a change in voltage, proportional to current, and inversely proportional to capacitance. The equation of a capacitor is dv/dt = i/c.
Why don't capacitors allow DC current to pass?
A capacitor allows AC (to pass through) because capacitors resist a change in voltage.. The capacitor need change resist in Input signal
What is the value of capacitor voltage and current after 5 time constant?
After 5 time constants, capacitor voltage/current will be about 99.3% of the input step change.
How could a capacitor have voltage but no current?
Voltage and current are two different things. Voltage is potential energy per charge, in joules per coulomb, while current is charge transfer rate, in coulombs per second. Its that same as saying that a battery has voltage but no current, because there is no load. Well, a capacitor resists a change in voltage by requiring a current to change the voltage. Once that voltage is achieved, there is infinite resistance to the voltage, and thus no current.
What does the continuity of capacitor voltage mean?
It might mean that the voltage across a capacitor cannot change instantanteously because that would demand an infinite current. The current in a capacitor is C.dV/dt so with a finite current dV/dt must be finite and therefore the voltage cannot have a discontinuity.
Why does the current lead the voltage across a capacitor by 90 degree rather than lag it?
A: Because a capacitor have to have time to charge to the voltage In a capacitor, the current depends on the voltage difference across it. On AC, this makes it charge, if the voltage is increasing above zero, and discharge if the voltage is reducing towards zero. Because a capacitor has almost no internal resistance, and most loads that it is connected to have only very small resistances in series with the capacitor, the charging and discharging currents depend pretty much on the rate at which the voltage is changing. At the zero crossing point of the sine-wave, when the voltage is actually zero, the rate of change of voltage is very high (the sine-wave is at its steepest), so the current is also very high. If the voltage is positive-going, the current is positive, and if the voltage is negative-going, the current is negative. At the peak of the voltage waveform, the rate of change of voltage is zero or very low (the sine-wave is flat, and not really changing its voltage) so the current is zero, too. Since the maximum positive current occurs when the voltage is passing through zero, going positive, and the maximum negative current happens when the voltage is passing through zero, going negative, the current peaks happen 90 degrees before the voltage peaks, so the current is said to lead the voltage. This is the same as saying the voltage lags the current by 90 degrees.
What is the phase relationship of voltage across a capacitor and current though the capacitor?
In a capacitor, the current LEADS the voltage by 90 degrees, or to put it the other way, the voltage LAGS the current by 90 degrees. This is because the current in a capacitor depends on the RATE OF CHANGE in voltage across it, and the greatest rate of change is when the voltage is passing through zero (the sine-wave is at its steepest). So current will peak when the voltage is zero, and will be zero when the rate of change of voltage is zero - at the peak of the voltage waveform, when the waveform has stopped rising, and is about to start falling towards zero.
Why voltage across capacitor cant change instantaneously?
Capacitors resist change in voltage. By definition, the equation is dv/dt = i/c, or rate of change of voltage in volts per second is current in amps divided by capacitance in farads. In order for the voltage to change instantaneously, then dv/dt must be infinity, which means i/c is also infinity. If capacitance is non-zero, then current must be infinity. Since there is no perfect voltage source, or no resistor or wire with perfect zero ohms, then it is impossible to have an infinite current, so it is impossible for the voltage across a capacitor to change instantaneously.
Is it true that an alternating current passing through a capacitor While a direct current can not Explain?
Then I'll try this. Just as V=IR is the fundamental equation relating voltage, current and resistance for a resistor circuit, the following equation relates voltace, current and capacitance for a capacitor: Or, if you are not familiar with that calculus term with the derivative, you can think of it as: I(t) = C * (change of voltage per time) So when you have DC, there is no change of voltage with respect to time, so there is zero current. When you have an AC voltage signal that varies across the capacitor with time, that equation lets you calculate the current that results through the capacitor. A capacitor is two surfaces near each other, but not touching. A direct current "sees" a capacitor as an open switch. It cannot pass through. An alternating current "induces" a charge in a capacitor and can pass through.
What is the reason behind the lag of current in inductor lead in capacitor?
The physics of the energy storage. In an inductor, the current must fight against the stored energy in the magnetic field which tries to keep the current unchanged. Any change in the current lags the voltage since the stored energy impacts the adjustment. Similarly, the "displacement" current in a capacitor leads the electric field buildup in a capacitor, causing the voltage to lag the current until the stored energy building up in the electric field stabilizes. Any change in the voltage is first preceded by a change in the displacement current.
Capacitance is the property of an electrical circuit that?
A capacitor resists a change in voltage, proportional to current, and inversely proportional to capacitance. The equation of a capacitor is dv/dt = i/c.
How can current lag or lead voltage in an AC circuit isn't current a function of voltage etc?
Current can lag or lead voltage in an AC circuit when the load is what we call reactive. The idea that current is purely a function of voltage only applies when working with DC, or when working with purely resistive loads, such as light bulbs and toasters. Not so, when dealing with motors and power supplies. What happens is that an inductor resists a change in current. That means that, given a particular voltage and current at a particular instant of time, if you change the voltage, the current will not immediately follow - it will lag - because the inductor is a stored energy device. Similarly, a capacitor resists a change in voltage, which means that if you change the current, the voltage will not immediately follow - it will lag - also because the capacitor is a stored energy device. Flip over current and voltage in the analysis of a capacitor, and you find that the current will lead the voltage, as opposed to the inductor's current lagging the voltage. This causes the phenomenon of power factor, which is basically the cosine of the phase angle between voltage and current. Power factor is the ratio of apparent power to true power.
Why don't capacitor discharge completely in an RC circuit?
Capacitors do not get "full" like a glass of water. The current into a capacitor is the rate of change of charge, so it's equal to C * dV/dt or something. If the voltage is constant, there's no current. If the voltage on both sides of the resistor is the same, there's no current through the resistor and hence into the capacitor, so that's the steady-state - what you call "full" - the capacitor charged to the supply voltage.
