# RC and RL(frequency and potential difference)

• SAT2400
In summary: For part 2, you are right that the potential difference, V, on an inductor is also a function of frequency. However, unlike the situation with a capacitor, there is actually a resistance (in the form of the inductance) present in the circuit, which means that the potential difference on an inductor decreases as the frequency increases. This is because at high frequencies, the inductance "decreases the time it takes for the current to flow around the loop", which means that the voltage across the inductor is smaller than at lower frequencies.Again, I'm not sure if this helps at all, but it should.hmm,,not really.For part 3, things are a bit more complicated
SAT2400

## Homework Statement

1.(RC in AC)What will happen to the potential difference on the capacitor as the frequency increases? In terms of the reactance of the capacitor, why might this happen?

2.(RL in AC) What will happen to the potential difference on the inductor as the frequency increases? In terms of the reactance of the inductor, why might this happen?

3. How might time constant and period determine the inductors potential difference?

4. How might time constant and period determine the capacitors potential difference?

XL= 2pif
V=IR
I= V/Z

## The Attempt at a Solution

I do not know how to find the relationships between f and potential difference on both capacitor and inductor..What equations should I use?? Please help me answering these 4 questions! Thanks

Hi SAT2400

For part 1, you know the impedance of a capacitor, right? You also know the impedance of a resistor (which is just its resistance). You know that they are in series (I assume?). If so, then you know that at any instant, the voltage drop across each has to add up to the voltage of the source (like in any series circuit). Does that help?

hmmm,,not quite...

Can you explain more in detail!?T_T

and how do I know the impedence? is it the resistance??

I have got values for Xc(ohm), Z(ohm), I(Amp), Vc(V), Vr(V) and Vs.
THank you

Okay, well the impedance, Z, of a component is just a complex number that describes the relationship between the complex (or "phasor") voltage across that component and the complex current through it. In general, this complex impedance has a real part, R, and an imaginary part, X, such that:

Z = R + jX

The real part, R, is just the resistance of the comonent, and the imaginary part, X, is called the "reactance." In the case of a capacitor or an inductor, there is NO resistance (no real part). The impedance is purely imaginary (or purely "reactive", to use the EE jargon):

ZC = jXC.

The nice thing about impedances, is that they allow us to use the same circuit analysis techniques for AC circuits as we do for DC circuits. If two components are in series, the total impedance is just the sum of the individual impedances: Z = Z1 + Z2 etc. The fact that the voltages and currents are oscillatory functions of time (which could potentially make things complicated) is neatly handled by the complex numbers and the phase information they contain. If you are learning about this stuff, all of what I just said should be in your notes or your book somewhere, and you should have an expression for XC as a *function* of omega so that you know how the impedance of a capacitor changes with frequency.

## 1. What is the difference between RC and RL circuits?

RC and RL circuits are both types of circuits that contain a resistor and a capacitor (RC) or a resistor and an inductor (RL). The main difference between them is that RC circuits use a capacitor to store and release energy, while RL circuits use an inductor to store and release energy. This results in different behaviors and characteristics of the circuits.

## 2. How does frequency affect RC and RL circuits?

The frequency of an AC power supply has a significant impact on both RC and RL circuits. In RC circuits, as the frequency increases, the capacitor has less time to charge and discharge, resulting in a decrease in the amplitude of the current and voltage. In RL circuits, as the frequency increases, the inductor has less time to build up and collapse its magnetic field, resulting in a decrease in the amplitude of the current and voltage.

## 3. What is the formula for calculating the potential difference in RC and RL circuits?

The formula for calculating the potential difference in RC circuits is V = V0cos(ωt), where V0 is the amplitude of the voltage, ω is the angular frequency, and t is time in seconds. In RL circuits, the formula is V = V0sin(ωt).

## 4. How do I calculate the frequency in RC and RL circuits?

The frequency in RC and RL circuits can be calculated using the formula f = 1/(2π√(LC)), where f is the frequency in hertz, L is the inductance in henries, and C is the capacitance in farads. This formula applies to both RC and RL circuits.

## 5. What are some real-world applications of RC and RL circuits?

RC and RL circuits have a wide range of real-world applications, including filters in electronic devices, audio amplifiers, and power supplies. RC circuits are commonly used in radio and television tuners, while RL circuits are used in electric motors and generators. They are also essential components in electronic devices such as computers, smartphones, and household appliances.

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