Series Circuit

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

1. In a series circuit, which of the parameters remain constant across all circuit elements such as resistor, capacitor and inductor?
a) Voltage
b) Current
c) Both voltage and current
d) Neither voltage nor current

Answer: b

Explanation: In a series circuit, the current across all elements remain the same and the total voltage of the circuit is the sum of the voltages across all the elements.

2. If there are two bulbs connected in series and one blows out, what happens to the other bulb?
a) The other bulb continues to glow with the same brightness
b) The other bulb stops glowing
c) The other bulb glows with increased brightness
d) The other bulb also burns out

Answer: b

Explanation: Since the two bulbs are connected in series, if the first bulb burns out there is a break in the circuit and hence the second bulb does not glow.

3. A voltage across a series resistor circuit is proportional to?
a) The amount of time the circuit was on for
b) The value of the resistance itself
c) The value of the other resistances in the circuit
d) The power in the circuit

Answer: b

Explanation: V=IR hence the voltage across a series resistor circuit is proportional to the value of the resistance.

4. Many resistors connected in series will?
a) Divide the voltage proportionally among all the resistors
b) Divide the current proportionally
c) Increase the source voltage in proportion to the values of the resistors
d) Reduce the power to zero

Answer: a

Explanation: In a series circuit, the current remains the same across all resistors hence the voltage divides proportionally among all resistors.

5. What is the voltage measured across a series short?
a) Infinite
b) Zero
c) The value of the source voltage
d) Null

Answer: b

Explanation: A short is just a wire. The potential difference between two points of a wire is zero hence the voltage measured is equal to zero.

6. What happens to the current in the series circuit if the resistance is doubled?
a) It becomes half its original value
b) It becomes double its original value
c) It becomes zero
d) It becomes infinity

Answer: a

Explanation: I=V/R. Hence if R=2R V=I/2R and I=I/2.

7. What is the value of x if the current in the circuit is 5A?
 

 

a) 15 ohm
b) 25 ohm
c) 55 ohm
d) 75 ohm

Answer: a

Explanation: Total voltage=sum of voltages across each resistor. =>150=10*5+5*5+5*x. Solving the equation, we get x=15 ohm.

 8. Find the voltage across 60 ohm resistance.

 

a) 72V
b) 0V
c) 48V
d) 120V

Answer: b

Explanation: The 60ohm resistance is shorted since current always choses the low resistance path. Voltage across short circuit is equal to zero, hence voltage across the resistor is 0.

9. Find the voltage across the 6 ohm resistor.

  

 

a) 150V
b) 181,6V
c) 27.24V
d) 54.48V

Answer: c

Explanation: Total current=150/(6+12+15)=4.55A. V across 6ohm=Total current x 

re-sistance=4.55×6=27.24V.

  

10. Find the current in the circuit.

 

a) 1 A
b) 2 A
c) 3 A
d) 4 A

Answer: b

Explanation: I=V/R. Total resistance = 20+40=60ohm. I=120V. I=120/60=2A.




11. In series, if one bulb goes out, others will

a)      stay on

b)      also turn off

c)      blow up

d)     heat up

Answer: b

12. In series circuit electrons in current when comes to second bulb after passing through first, have

a)      more energy

b)      less energy

c)      more power

d)     less power

Answer: b

13. Adding more bulbs to a circuit with one battery would

a)      make them brighter

b)      make them sharper

c)      make them dimmer

d)     make them colorless

Answer: c

14.	What is the current flow through R1, R2, and R3?
	a) 1A, 1A, 1A b) 1A, 2A, 3A c) 3A, 3A, 3A d) 3A, 2A, 1A Answer: a Explanation: V = IR V = I(R1 + R2 + R3) I = V/(R1 + R2 + R3) = 9/(3 + 3 + 3) = 9/9 = 1 Amp.
15.	One of the most common applications of a potentiometer is as an adjustable voltage divider, also known as
	a) voltage control b) current control c) volume control      d) divider control Answer: c
16.	If the resistance total in a series circuit doubles, current will:
	a)  be the same b) be doubled c) reduce source voltage d) be halved Answer: d
17.	Power is defined as:
	a) the rate at which work is done b) work c) the conversion of energy d) joules Answer: a
18. With a total resistance of 3300 ohms and a 45 V source, if R3 is 1200 ohms, what will be its     voltage drop?
a       a) 16.36V       b) 32.72V       c) 10.90V       d) 15.00V        Answer: a
19.	Calculate the voltage at point B in the given circuit.
	a)    +10.48 V b) +0.94 V c) +2.6 V d) +3 V Answer: a

20 .	In the given circuit, what type of failure will cause the voltage at point B to equal the voltage at point C?
	a)  R1 shorts b) R2 shorts c) R3 shorts       d)     R2 opens Answer: b
21.	An 8-ohm resistor is in series with a lamp. The circuit current is 1 A. With 20 V applied,  what voltage is being allowed for the lamp?
	a)  4 V b)  8 V c)  12 V      d)  20 V Answer: c

22. What is wrong, if anything, with this circuit?
	a)     R1 is open. b) R1 is shorted. c) R2 is open. d) R2 is shorted. Answer: b

23.	Kirchhoff’s voltage law states that:
	a)  the sum of the voltage drops in a series circuit is equal to the total applied voltage b)  the algebraic sum of the resistances is equal to the sum of the voltages c)  the algebraic sum of the individual currents around a closed loop is zero d)  the voltages developed across each element in a series circuit are identical Answer: a
24.	If series current doubles, then:
	a)  resistance is halved b)  voltage is doubled c)  voltage is reduced      d)  resistance is doubled Answer: a

25.	A short circuit has:
	a)  too much resistance b)  no conductance c)  no resistance      d)  low current Answer: c
26.	If three resistors of 1.5 kilohms, 470 ohms, and 3300 ohms are in series with a 25-volt source, what is the total circuit current?
	a)  210 mA b)  5.2 mA c)  4.7 mA      d)  0.007 A Answer: C
27.	What is the total power in the circuit?
	a)  170 mW b)  1.7 W c)  17 W      d)  170 W Answer: a

28.	A string of resistors in a series circuit will:
	a)  divide the source voltage in proportion to their values b)  reduce the power to zero c)  cause the current to divide      d)  increase the source voltage in proportion to the values Answer: a

29.	While putting three 1.5 V batteries into a flashlight, you put one in backwards.  The flashlight will be ______________.       a)  brighter than normal b)  dimmer than normal c)  Off      d)  the same Answer: b
	30. In a series circuit, the voltage measured across a short will be:
	a)  source voltage      b)  infinite voltage      c)  zero volts           d)  the normal voltage drop Answer:  C
	31. A series circuit current:
	a)  remains the same through each component      b)  is the same as the individual resistances      c)  is subtracted by each component           d)  varies through each component Answer: a
	32. Which equation determines individual resistor voltage drop?
	a)  V x R       b)  I2 x R       c)  V x I            d)  I x R Answer: d
33.	How will an open resistor affect a series circuit?
	a)  Current will flow around the open resistor. b)  The open resistor will drop 0 V. c)   Total resistance will decrease.      d)  No current will flow in the circuit. Answer: d
34.	The voltage drop across a series resistor is proportional to what other value?
	a)  total resistance b)  its own resistance c)   wattage rating      d)   the amount of time the circuit is on Answer: b
35.	Resistance in a series circuit will:
	a)  control the voltage b)  double the current       c)  halve the power d)  oppose current Answer: d
36.	When a battery is connected to a series circuit, it delivers current based only upon:
	a)  primary/secondary difference b)  total resistance c)  the polarity connections      d)  average resistance Answer: b
37.	What determines the total resistance in a series circuit?
	a)  the largest resistor b)  the sum of the resistors c)  the largest resistor minus the smaller      d)  the smallest resistor Answer: b
38.	If two resistors have the same voltage drop in a series circuit, it means:
	a)  they are connected in parallel b)  they are of unequal value c)  the voltage has doubled      d)  they are of equal value Answer: d

 

39.	If series resistors dissipate 16 mW, 107 mW, 146 mW, and 243 mW, what is the total power consumed by the circuit?
	a)  128 mW b)  269 mW c)  512 mW      d)  1024 mW Answer: c

40.	A series circuit schematic is recognized because all the components are connected:
	a)  diagonally across the page b)  in a uniform vertical manner c)  end to end in a "string"      d)  horizontally across the page Answer: C

41.	With a 900 V source, voltage is divided across 3 series resistors of 300 V, 280 V, and:_____?
	a)  30 V b)  270 V c)  320 V      d)  900 V Answer: C Explanation: Total Voltage (V) = V1+V2+V3                                     900 = 300 + 280 + V3                                      V3= 900 - 300 – 280 = 320