Four wires meet at a junction P. A current of 5 A flows towards P in the first wire, a current of 2 A flows away from P in the second wire and a current of 1 A flows towards P in the third wire. The current in the fourth wire is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4 A, flowing away from P
By Kirchhoff’s junction rule, the sum of the currents flowing towards a junction equals the sum of the currents flowing away from it. Each current has to be taken with its direction.
The currents flowing towards P add up to:
\( \begin{aligned} I_{\mathrm{in}} &= 5\,\mathrm{A}+1\,\mathrm{A} \\ &= 6\,\mathrm{A} \end{aligned} \)
Only 2 A is known to flow away from P, so the fourth wire must carry the rest away:
\( 6\,\mathrm{A}=2\,\mathrm{A}+I_4 \)
\( \Rightarrow\; I_4=4\,\mathrm{A} \)
Hence, a current of 4 A flows away from P in the fourth wire.
NCERT (2026-27):
Kirchhoff’s Rules – “(a) Junction rule: At any junction, the sum of the currents entering the junction is equal to the sum of currents leaving the junction …”