There were 4 sets of questions in the mid-term test. However, the questions were identical in 4 sets and they differ only in values of resistance and sources. Solution is given for Set A only.

EG1108 – Electrical Engineering / Page 2

Q.1 Consider the circuit below with R1= 10 Ω, R2= 15 Ω, R3= 20 Ω, R4= 5 Ω, and I4= 0.1 A. Find VS using Ohm’s law, KVL and KCL.

I4 = 0.1 A Voltage across R4 → R4I4 = (5)(0.1) = 0.5 V Same voltage appears across R2 and R3. Current through R3 → (0.5V)/20Ω = 0.025 A Current through R2 → (0.5V)/15Ω = 0.033 A Current through R1 → 0.1+0.025+0.033 = 0.158 A VS = (0.158)(R1) + 0.5 = (0.158)(10) + 0.5 = 2.08 V

There were 4 sets of questions in the mid-term test. However, the questions were identical in 4 sets and they differ only in values of resistance and sources. Solution is given for Set A only.

EG1108 – Electrical Engineering / Page 3

Q.2 Write a set of node voltage equations for the circuit shown below. [R1= 10 Ω, R2= 10 Ω, R3= 10 Ω, R4= 10 Ω, IS= 2 A]. Do not solve the simultaneous equations.

, 2

2 , → 2 → 2 20 Node V1:

Node V2:

0 → 0 → 3 0

2 0 → 3 0 → 4 3 0 Node V3:

There were 4 sets of questions in the mid-term test. However, the questions were identical in 4 sets and they differ only in values of resistance and sources. Solution is given for Set A only.

EG1108 – Electrical Engineering / Page 4

Q.3 (a) Find Thevenin’s equivalent between nodes ‘x’ and ‘y’ of the circuit shown below. [Vin= 4 V, Rin= 240 Ω, Ro= 20Ω]

(b) If a load is connected between ‘x’ and ‘y’, what is the maximum power delivered to that load?

(a) Find VOC:

Vin

Rin

Ro6iVOC

i

+

-

x

VOC

+

-y

6 120

4240

120 , → 4 V

Find ISC:

Vin

Rin

Ro6iVxy = 0

i

+

-

x

y

ISC

6

4 0240

160

6 ,

There were 4 sets of questions in the mid-term test. However, the questions were identical in 4 sets and they differ only in values of resistance and sources. Solution is given for Set A only.

V O -4 V Th =V C =

40 Ω

(b)

For maximum power transfer, R h L = RT

So, load c rr →u ent 5 A 0.0

Power → 0.05 40 0.1W

There were 4 sets of questions in the mid-term test. However, the questions were identical in 4 sets and they differ only in values of resistance and sources. Solution is given for Set A only. EG1108 – Electrical Engineering / Page 5

Q.4 Find the voltage Vab using superposition theorem. [R1= 5 Ω, R2= 10 Ω, R3= 5 Ω, I1= 12 A, V1= 120 V, I2= 10 A]

5

10

512 10120

a

b

12 .. . .

2.4 A , 2.4 10 24 V

|| .9.6 A

. 4.8 A, , 5 24 V

10 .. . .

2.0 A , 2.0 10 20 V

, , , 24 24 20 20