Electrical RLC Quiz Ex part 1

In the impedance triangle of an RC circuit, what does the vertical value represent?

• Resistance

• Capacitance

• Inductive Reactance

• Capacitive Reactance

Answer explanation

In the impedance triangle of an RC circuit, the vertical value represents Capacitive Reactance. This is the opposition that a capacitor offers to the flow of alternating current, distinguishing it from resistance and inductive reactance.

What is the formula for calculating total capacitance (CT) in a parallel circuit?

• CT = C1 + C2 + C3

• CT = C_1 \times C_2 \times C_3

Answer explanation

In a parallel circuit, the total capacitance (CT) is calculated by simply adding the individual capacitances together: CT = C1 + C2 + C3. This is because capacitors in parallel share the same voltage and their capacitances add directly.

What is the effect of increasing resistance (R) in an RL series circuit on the total impedance (Z) and phase angle \( \phi \)?

• Impedance decreases; phase angle decreases.

• Impedance decreases; phase angle increases.

• Impedance increases; phase angle increases.

• Impedance increases; phase angle decreases.

Answer explanation

In an RL series circuit, increasing resistance (R) raises the total impedance (Z) due to the formula Z = √(R² + (XL)²). The phase angle (φ) decreases as the circuit becomes more resistive, leading to less reactive influence.

In a parallel resistive circuit, when one resistor is removed, the total resistance:

• Increases

• Decreases

• Remains the same

• Becomes zero

Answer explanation

In a parallel resistive circuit, removing one resistor increases the total resistance because the remaining resistors provide less overall current path, leading to a higher equivalent resistance.

What is the primary reason for maintaining a high power factor in industrial plants?

• To increase energy consumption

• To reduce line current and improve system efficiency

• To decrease voltage levels

• To increase system downtime

Answer explanation

Maintaining a high power factor reduces line current, which minimizes losses in the electrical system and improves overall efficiency. This is crucial for industrial plants to optimize energy use and reduce costs.

Calculate the total inductive reactance for two inductors in series, L1=4 H and L2=6 H, in an AC circuit operating at a frequency of 50 Hz.

• 3140 Ω

• 3142 Ω

• 2000 Ω

• 5000 Ω

Answer explanation

The total inductive reactance (X_L) for inductors in series is given by X_L = 2πf(L1 + L2). For L1=4 H, L2=6 H, and f=50 Hz, X_L = 2π(50)(10) = 3142 Ω. Thus, the correct answer is 3142 Ω.

If two capacitors with values 10 µF and 20 µF are connected in parallel, what is the total capacitance?

• 10 µF

• 15 µF

• 30 µF

• 5 µF

Answer explanation

When capacitors are connected in parallel, their capacitances add up. Therefore, the total capacitance is 10 µF + 20 µF = 30 µF, making the correct answer 30 µF.

In a series circuit with R1=5 Ω and R2=10 Ω, connected to an AC source, the phase difference between voltage and current is:

• 90°

• 45°

• 0°

• 180°

Answer explanation

In a series circuit with only resistors (R1 and R2), the voltage and current are in phase, resulting in a phase difference of 0°. Therefore, the correct answer is 0°.

How do you calculate the total current in a parallel RLC circuit?

• Add the branch currents directly in magnitude.

• Add the branch currents vectorially at their respective phase angles.

• Subtract the branch currents directly in magnitude.

• Subtract the branch currents vectorially at their respective phase angles.

Answer explanation

In a parallel RLC circuit, the total current is the vector sum of the branch currents, considering their phase angles. This is because the currents can be out of phase due to the reactive components, making vector addition necessary.

In a series RC circuit, what is the total opposition to current called?

• Resistance

• Reactance

• Impedance

• Conductance

Answer explanation

In a series RC circuit, the total opposition to current is called impedance. It combines both resistance and reactance, representing the overall effect on current flow.