CBSE Class 12 Physics 2013 Paper

Question : 16 of 29

Marks: +1, -0

Use Kirchhoff's rules to determine the value of the current

I_1

flowing in the circuit shown in the figure.

Solution:

The given circuit:

At node

{\M}

, applying

{\KCL}

I_3=I_1+I_2

In loop MPQN, applying KVL,

\;20 I_3+30 I_1\;=20

\;\text " Or, "\;\;20 (I_1+I_2) +30 I_1\;=20

\;\text " Or, "\;\;50 I_1+20 I_2\;=20

\;\text " Or, "\;\;5 I_1+2 I_2\;=2

.......(i)
In loop MSTN, applying KVL,

\;-20 I_2-20 I_3\;=-20-80=-100

\;\text " Or, "\;\;-20 I_2-20 (I_1+I_2) \;=-100

\;\text " Or, "\;\;-20 I_1-40 I_2\;=-100

\;\text " Or, "\;\;-I_1-2 I_2\;=-5

.......(ii)
Solving equations (i) and (ii)

I_1=-\;{3}/{4} A

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