Kirchhoff's Junction Rule
At a junction in a network, currents of 5 A and 3 A enter while currents of 4 A and I leave through separate branches, so what is I?
Select the correct option:
Solution
4 A
Kirchhoff's junction rule, a consequence of charge conservation, requires that the total current flowing into a node equals the total current flowing out, as formalised in NCERT Class 12, Chapter 3 (Current Electricity). No charge can accumulate at a point, so summing the entering currents gives 5+3=8 A, and the leaving currents must also total 8 A. Since one exit branch carries 4 A, the remaining branch carries I=8−4=4 A. The option 12 A wrongly adds all listed currents together without balancing directions. The option 2 A incorrectly subtracts the 3 A input from a partial sum. The option 8 A forgets that 4 A already leaves and assumes the whole incoming current exits through one branch. A consistency check confirms the balance: inflow 5+3=8 A equals outflow 4+4=8 A, so charge is conserved at the junction and the sign and magnitude are both physically sound.
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About This Question
- Subject
- physics
- Chapter
- current electricity
- Topic
- kirchhoff's junction rule
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
4 A
Kirchhoff's junction rule, a consequence of charge conservation, requires that the total current flowing into a node equals the total current flowing out, as formalised in NCERT Class 12, Chapter 3 (Current Electricity). No charge can accumulate at a point, so summing the entering currents gives 5+3=8 A, and the leaving currents must also total 8 A. Since one exit branch carries 4 A, the remaining branch carries I=8−4=4 A. The option 12 A wrongly adds all listed currents together without balancing directions. The option 2 A incorrectly subtracts the 3 A input from a partial sum. The option 8 A forgets that 4 A already leaves and assumes the whole incoming current exits through one branch. A consistency check confirms the balance: inflow 5+3=8 A equals outflow 4+4=8 A, so charge is conserved at the junction and the sign and magnitude are both physically sound.
This easy difficulty physics question is from the chapter current electricity, covering the topic of kirchhoff's junction rule. It appeared in the 2025 exam.
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