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NCERT Class XII Chapter
Current Electricity
Questions With Solutions

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Question : 9 of 24
Marks: +1, -0
Determine the current in each branch of the network shown in figure.
Solution:  
Let us first distribute the current in different branches.
Now, equations for different loops using Kirchhoff’s II law,
Loop 1
ΣE = ΣIR
10I1+5Ig−5I210I_1+5I_g-5I_2 = 0
or 2I1+Ig−I22I_1+I_g-I_2 = 0 ... (i)
Loop 2
ΣE = ΣIR
5Ig+10[I2+Ig]−5[I1−Ig]5I_g + 10[I_2+I_g] - 5[I_1-I_g] = 0
10I2+20Ig−5I110I_2 + 20I_g-5I_1 = 0
or 2I2+4Ig−I12I_2+4I_g-I_1 = 0 ... (ii)
Loop 3
5I2+10(I2+Ig)+10I5I_2+10(I_2+I_g)+10I = 10
15I2+10Ig+10I15I_2+10I_g+10I = 10
or 3I2+2Ig+2I3I_2+2I_g+2I = 2 ... (iii)
Solving equations (i) and (ii)
2I1+Ig−I22I_1+I_g-I_2 + 2 [−Ii+4Ig+2I2][-I_i+4I_g+2I_2] = 0
or 9Ig+3I29I_g+3I_2 = 0 or I2I_2 = - 3 IgI_g ... (iv)
In the loop ABCDA
10I1+5[I1−Ig]10I_1+5[I_1-I_g] - 10 [I2+Ig][I_2+I_g] - 5I25I_2 = 0
15I1−15I2−15Ig15I_1-15I_2-15I_g = 0 or I1−I2−IgI_1-I_2-I_g = 0 ... (v)
Solving equations (ii) and (v)
2I2+4Ig−I12I_2+4I_g-I_1 = 0 or 2(I1−I2−Ig=0)2(I_1-I_2-I_g=0)
or 2Ig+I12I_g+I_1 = 0 or I1I_1 = - 2 IgI_g ... (vi)
Now using the result of (iv) and (vi) in equation (iii)
3I2+2Ig+2I3I_2+2I_g+2I = 2 - 3[3Ig]+2Ig3[3I_g] + 2I_g + 2I = 2 or 2I - 7Ig7I_g = 2 ... (vii)
Using Kirchhoff’s law, I = I1+I2I_1+I_2 ⇒ I = - 5Ig5I_g
So, equation (vii)
2[−5Ig]−7Ig2[-5I_g] - 7I_g = 2 or −17Ig-17I_g = 2
So, finally IgI_g = - 2/17 A and I = +1017\frac{+10}{17} A. Also I1I_1 = 417\frac{4}{17} A , I2I_2 = 617\frac{6}{17} A
Current in branch AB = 417\frac{4}{17} A , Current in branch AD = 617\frac{6}{17} A
Current in branch BD = −217\frac{-2}{17} A , Current in branch BC = 617\frac{6}{17} A
Current in branch DC = 417\frac{4}{17} A
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