A 217 Ω resistor, a 0.875 H inductor, and a 6.75 μF capacitor are connected in series across a voltage source that has voltage amplitude 30.0 V and an angular frequency of 220 rad/s . What is v at t= 22.0 ms ? What is vR at t= 22.0 ms ? What is vL at t= 22.0 ms ? What is vC at t= 22.0 ms ? What is vR? What is vL? What is vC?

Respuesta :

For an AC circuit:

I = V/Z

V = AC source voltage, I = total AC current, Z = total impedance

Note: We will be dealing with impedances which take on complex values where j is the square root of -1. All phasor angles are given in radians.

For a resistor R, inductor L, and capacitor C, their impedances are given by:

[tex]Z_{R}[/tex] = R

R = resistance

[tex]Z_{L}[/tex] = jωL

ω = voltage source angular frequency, L = inductance

[tex]Z_{C}[/tex] = -j/(ωC)

ω = voltage source angular frequency, C = capacitance

Given values:

R = 217Ω, L = 0.875H, C = 6.75×10⁻⁶F, ω = 220rad/s

Plug in and calculate the impedances:

[tex]Z_{R}[/tex] = 217Ω

[tex]Z_{L}[/tex] = j(220)(0.875) = j192.5Ω

[tex]Z_{C}[/tex] = -j/(220×6.75×10⁻⁶) = -j673.4Ω

Add up the impedances to get the total impedance Z, then convert Z to polar form:

Z = [tex]Z_{R}[/tex] + [tex]Z_{L}[/tex] + [tex]Z_{C}[/tex]

Z = 217 + j192.5 - j673.4

Z = (217-j480.9)Ω

Z = (527.6∠-1.147)Ω

Back to I = V/Z

Given values:

V = (30.0∠0+220t)V (assume 0 initial phase, and t = time)

Z = (527.6∠-1.147)Ω (from previous computation)

Plug in and solve for I:

I = (30.0∠0+220t)/(527.6∠-1.147)

I = (0.0569∠1.147+220t)A

To get the voltages of each individual component, we'll just multiply I and each of their impedances:

[tex]v_{R}[/tex] = I×[tex]Z_{R}[/tex]

[tex]v_{L}[/tex] = I×[tex]Z_{L}[/tex]

[tex]v_{C}[/tex] = I×[tex]Z_{C}[/tex]

Given values:

I = (0.0569∠1.147+220t)A

[tex]Z_{R}[/tex] = 217Ω = (217∠0)Ω

[tex]Z_{L}[/tex] = j192.5Ω = (192.5∠π/2)Ω

[tex]Z_{C}[/tex] = -j673.4Ω = (673.4∠-π/2)Ω

Plug in and calculate each component's voltage:

[tex]v_{R}[/tex] = (0.0569∠1.147+220t)(217∠0) = (12.35∠1.147+220t)V

[tex]v_{L}[/tex] = (0.0569∠1.147+220t)(192.5∠π/2) = (10.95∠2.718+220t)V

[tex]v_{C}[/tex] = (0.0569∠1.147+220t)(673.4∠-π/2) = (38.32∠-0.4238+220t)V

Now we have the total and individual voltages as functions of time:

V = (30.0∠0+220t)V

[tex]v_{R}[/tex] = (12.35∠1.147+220t)V

[tex]v_{L}[/tex] = (10.95∠2.718+220t)V

[tex]v_{C}[/tex] = (38.32∠-0.4238+220t)V

Plug in t = 22.0×10⁻³s into these values and take the real component (amplitude multiplied by the cosine of the phase) to determine the real voltage values at this point in time:

V = 30.0cos(0+220(22.0×10⁻³)) = 3.82V

[tex]v_{R}[/tex] = 12.35cos(1.147+220(22.0×10⁻³)) = 11.8V

[tex]v_{L}[/tex] = 10.95cos(2.718+220(22.0×10⁻³)) = 3.19V

[tex]v_{C}[/tex] = 38.32cos(-0.4238+220(22.0×10⁻³)) = -11.2V

The root mean square voltage (Vrms) of the circuit is 29.76 V.

The voltage in the inductor (VL) is 19.83 V.

The voltage in the capacitor (Vc) is 0.069V.

The voltage in the resistor (VR) is 22.35 V.

Rms voltage of circuit

The rms voltage is calculated as follows;

V(rms) = -V₀sin(ωt)

V(rms) = -30 x sin(220 x 22 x 10⁻³)

V(rms) = 29.76 V

Impedance of the circuit

The overall opposition to the flow of current is calculated as follows;

Xl = ωL

Xl = 220 x 0.875 = 192.5 ohms

Xc = 1/ωC

Xc = (1) / (220 x 6.75 x 10⁻³)

Xc = 0.673 ohm

[tex]Z = \sqrt{R^2 + (X_l - X_c)^2} \\\\Z = \sqrt{217^2 + (192.5- 0.673)^2}\\\\Z = 289.63 \ ohm[/tex]

Current flowing in the series circuit

[tex]I_{rms} = \frac{V_{rms}}{Z} \\\\I_{rms} = \frac{29.76}{289.63} \\\\I_{rms} = 0.103 \ A[/tex]

Voltage in inductor

VL = IXl

VL = (0.103) x 192.5

VL = 19.83 V

Voltage in capacitor

Vc = IXc

Vc = 0.103 x 0.673

Vc = 0.069 V

Voltage in resistor

VR = IR

VR = 0.103 x 217

VR = 22.35 V

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