A series combination of resistors is the one in which resistors are connected end by the end. One terminal of the resistor connects to the other terminal of the resistor and the chain continues.

On the other hand in the parallel circuit, all parallel resistors have one terminal shorted at one point, while other terminal shorted at other points.

Given below are the Basic MCQ questions on Series and Parallel resistors.

## Two series resistors of 5 ohms in parallel to two series resistors of 5 ohms

What is the equivalent resistance of two series resistors of 5 ohms that are connected in parallel to two series resistors of 5 ohms:

- 2.5 ohms
- 5 ohms
- 10 ohms
- 20 ohms

Correct answer: 2. 5 ohms

Explanation: *R _{eq} = (5 + 5) || (5 + 5) = 10 || 10 = 5*

## Three series resistors having equivalent resistance of 15 ohms

Three series resistors have an equivalent resistance of 15 ohms. The first resistor has a resistance of 3 ohms, While the second has 5 ohms. What’s the resistance of the third resistor:

- 5 ohms
- 6 ohms
- 7 ohms
- 8 ohms

Correct answer: 3. 7 ohms

Explanation: Let equivalent resistance is Req = 15 ohms

R1 = 3 ohms & R2 = 5 ohms R3 = X

Req = R1 + R2 + R3

Req = 3 + 5 + X

X = 15 – 3 – 5 = **7 ohms** which is correct answer

*Good to know: Ohm’s is SI unit of resistance*

## A series circuit having two series resistors has 5 mA current

A series circuit having two series resistors has 5 mA current when connected to a 10 V source. The resistance of the first resistor is 1.5k ohms. What is the resistance of the second resistor:

- 0.5k ohms
- 1k ohms
- 1.5k ohms
- Can’t predict

Correct answer: 1. 0.5k ohms

From Ohm’s law: I = V/R; Or R = V/I

For the series circuit of present case R = R1 + R2

R1 + R2 = V/I = 10 V/5 mA

R1 + R2 = 2 kohm

1.5 kohm + R2 = 2 kohm

**R2 = 0.5 kohm** which is correct answer

## Four resistors (all having resistance 5 ohms) should be connected in which way to obtain R(eq) = 5 ohms

Four resistors (all having resistance 5 ohms) should be connected in which way to obtain R(eq) = 5 ohms:

- Sum all
- One in parallel to sum of three
- Two in series are parallel to other two in series
- Two in parallel to series of other two

Correct answer: 3. Two in series are parallel to other two in series

Explanation: R + R || R + R

5 Ω + 5 Ω || 5 Ω + 5 Ω

10 Ω || 10 Ω = 5 Ω

MCQ on different Electrical Engineering Topics

## To reduce 500 ohms resistance to 250 ohms

A 500 Ω resistance is connected in a circuit. It is desired to reduce its resistance to 250 Ω. The value of resistance to be connected in parallel will be:

- 187.5 Ω
- 250 Ω
- 500 Ω
- 750 Ω

Correct answer: 3. 500 ohms

A resistance of 500 ohms should be connected in parallel to 500 ohms so as to obtain 250 ohms

*Good to know. If ‘n’ number of resistors having the same value of resistance are connected in parallel, then R _{eq} = R/n*

Where R is resistance of one resistor and n is total number of resistors.

R_{eq} = 1/(1/500 + 1/500) = 250 ohms