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• If we apply an AC voltage, the frequency of the voltage affects the amount of current that will flow.

• Inductors, capacitors, and resistors all react differently to AC voltage.

• But, in all three cases, the frequency of the AC current will be exactly equal to the frequency of the voltage.

• Let us call the voltage at this point the "Input Voltage".

• This is the voltage that we control.

• In the case of an ideal resistor,

• the current that flows is always proportional to the difference in the voltage values at the two sides of the resistor.

• This means that if the only components in our circuits are ideal resistors,

• then the amplitude of the current that flows is independent of the voltage's frequency.

• Now, suppose we replace the resistor on the right with a capacitor.

• Once the capacitor is charged, both sides of the resistor will have the same voltage, and no current will flow.

• Current flows only if we change the value of the input voltage.

• The amount of current that flows depends on the difference in the voltage values of the two sides of the resistor.

• If we change the value of the input voltage slowly,

• then the voltage values of the two sides of the resistor will tend to stay at about the same voltage.

• This means that only a small amount of current will flow through this circuit at low frequency.

• At high frequency, a larger amount of current will flow.

• This is because if we vary the input voltage quickly as shown,

• the capacitor never has enough time to charge, and the voltage across it always stays close to zero.

• Having a voltage across the capacitor that is always close to zero

• allows a larger voltage difference between the two ends of the resistor, allowing more current to flow.

• Since the voltage across the capacitor does not have the ability to change instantaneously,

• the voltage across the capacitor changes after the current changes.

• Let's turn off the input voltage.

• Now let's replace the capacitor with an inductor.

• An inductor exerts a force preventing the current flowing through it from changing instantaneously.

• If the input voltage is constant, then the inductor will not exert any forces, and it will therefore not impede the flow of current.

• If the input voltage changes, the inductor will initially try to keep the current through it at the same value as before.

• After we change the voltage, we need to wait for the current to change.

• After the current changes, the inductor then wants to keep the current at this new value.

• If we change the input voltage very rapidly as shown, the current will not have enough time to change.

• This means that only a small amount of current will flow through the inductor at high frequency.

• At low frequency, more current will flow.

• In this sense, an inductor has the opposite behavior of a capacitor.

• Also, whereas the voltage across a capacitor can't change instantaneously,

• for an inductor it is the current that can't change instantaneously.

• This means that for an inductor, the current changes after the voltage changes.

• The frequency of the input voltage is only one of the factors that determines how much the inductor will impede the flow of current.

• Another factor is the amount of inductance the inductor has.

• If the inductor has a higher inductance, then a smaller amount of AC current will flow through it.

• This is because with a higher inductance,

• the inductor will exert a greater force trying to keep the current flowing through it constant.

• In this example, even though we have a low frequency,

• we still have a small amount of AC current flowing due to the fact that the value of the inductance is high.

• Increasing the capacitance of a capacitor has the opposite effect of increasing the inductance of an inductor.

• If a capacitor has a higher capacitance, then a larger amount of AC current will flow through it.

• This is due to the fact that with a higher capacitance, the capacitor charges and discharges more slowly.

• Therefore, in this case, the voltage across the capacitor stays close to zero,

• thereby allowing a larger difference in voltage to develop at the two ends of the resistor,

• thereby allowing more current to flow.

If we apply an AC voltage, the frequency of the voltage affects the amount of current that will flow.

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B1 INT US voltage current capacitor resistor frequency flow

# AC current impedance - Alternating Voltage for inductors, capacitors

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