This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Resistance and Capacitance in Series”.

1. In an RC series circuit ________

a) Applied voltage lags capacitor voltage

b) Applied voltage leads capacitor voltage

c) Current and voltage are in phase

d) Applied voltage and capacitive voltage are in phase

View Answer

Explanation: In an RC circuit, the applied voltage leads the current in the circuit, hence the applied voltage leads the capacitive voltage.

2. Which, among the following is the correct expression for φ?

a) φ=tan^{-1}(Xc/R)

b) φ=tan^{-1} (R/Xc)

c) φ=tan^{-1} (Xc*R)

d) φ=cos^{-1} (Xc/R)

View Answer

Explanation: Form the impedance triangle, we get tanφ= Xc/R.

Hence φ=tan

^{-1}(Xc/R).

3. For an RC circuit, the phase angle is always ________

a) Positive

b) Negative

c) 0

d) 90

View Answer

Explanation: For a series resistance and capacitance circuit, the phase angle is always a positive value because the current will always leads the voltage.

4. What is φ in terms of voltage?

a) φ=cos^{-1}V/VR

b) φ=cos^{-1}V*VR

c) φ=cos^{-1}VR/V

d) φ=tan^{-1}V/VR

View Answer

Explanation: Form the voltage triangle, we get cosφ= VR/V.

Hence φ=cos

^{-1}VR/V.

5. An RC network is one which consists of?

a) Resistor and capacitor in parallel

b) Resistor and capacitor in series

c) Resistor and inductor in parallel

d) Resistor and inductor in series

View Answer

Explanation: An R-C network is a network which consists of a resistor which is connected in series to a capacitor.

6. At DC, capacitor acts as?

a) Open circuit

b) Short circuit

c) Resistor

d) Inductor

View Answer

Explanation: At DC, the inductor acts as short circuit because the capacitive resistance is infinity. The frequency of a DC circuit is 0. The capacitive resistance=1/(2*pi*f*C). Therefore, if the frequency is 0, the capacitive resistance is infinity and it acts as an open circuit.

7. In an RC series circuit, when the switch is closed and the circuit is complete, what is the response?

a) Response does not vary with time

b) Decays with time

c) Increases with time

d) First increases, then decreases

View Answer

Explanation: In an RC series circuit, the response decays with time because according to the equation, there is an exponential decrease in the response.

8. The expression for current in an RC circuit is?

a) i=(V/R)e^{(t/RC)}

b) i=(V/R)e^{(-t/RC)}

c) i=(V/R)/e^{(t/RC)}

d) i=(V/R)/e^{(-t/RC)}

View Answer

Explanation: The particular solution of the current equation is zero. Hence, the expression for the current in an RC circuit is:

i=(V/R)e

^{(-t/RC)}.

9. An 8microF capacitor is connected in series with a 0.5 megaohm resistor. The DC voltage supply is 200V. Calculate the initial charging current.

a) 100 microA

b) 500 microA

c) 400 microA

d) 1000microA

View Answer

Explanation: In a series RC circuit, the initial charging current is:

I=V/R= 200/(0.5*10

^{6})= 400*10

^{-6}A= 400 microA.

10. While discharging, what happens to the current in the capacitive circuit?

a) Decreases linearly

b) Increases linearly

c) Decreases exponentially

d) Increases exponentially

View Answer

Explanation: The equation for the value of current in a discharging capacitive circuit is:

I=I0*e-t/RC. From this equation, we can see that the current is exponentially decreasing since e is raised to a negative power.

**Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.**

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