Question : Use Kirchhoff's rules to find the current through 3 Ω resistor in the circuit shown in the figure :

Doubt by Riddhi & Ridhi
Solution :

Applying Kirchhoff's Loop Rule in closed loop 1
-3(I2-I1)+4I1=3
-3I2+3I1+4I1=3
7I1-3I2=3 — (1)
-3(I2-I1)+4I1=3
-3I2+3I1+4I1=3
7I1-3I2=3 — (1)
Again, applying Kirchhoff's Loop Rule in closed loop 2
2I2+3(I2-I1)=5
2I2+3I2-3I1=5
-3I1+5I2=5 — (2)
On solving equation (1) and (2)
[7I1-3I2=3 ] × 3
[-3I1+5I2=5] × 7
2I2+3I2-3I1=5
-3I1+5I2=5 — (2)
On solving equation (1) and (2)
[7I1-3I2=3 ] × 3
[-3I1+5I2=5] × 7
21I1-9I2=9
-21I1+35I2=35
Adding the above equations
-21I1+35I2=35
Adding the above equations
0+26I2=44
26I2=44
I2=44/26
I2=22/13 A
Putting in equation (1)
7I1-3(22/13)=3
7I1-66/13=3
7I1=3+66/13
7I1=(39+66)/13
7I1=105/13
I1=105/(13×7)
I1=15/13 A
26I2=44
I2=44/26
I2=22/13 A
Putting in equation (1)
7I1-3(22/13)=3
7I1-66/13=3
7I1=3+66/13
7I1=(39+66)/13
7I1=105/13
I1=105/(13×7)
I1=15/13 A
Current through 3 Ω resistor
= I2-I1
= 22/13-15/13
= 7/13 A
= 0.54 A
= I2-I1
= 22/13-15/13
= 7/13 A
= 0.54 A
Hence, the current through 3Ω resistor is (7/13) A or 0.54 A from E to B.