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Class 12 › Physics › Current Electricity
CBSE2023Class Class 12 · Physics5 Marks · Long✅ Verified
(I) Currents $I_1$, $I_2$, $I_3$ at a junction satisfy $I_1 = I_2 + I_3$.
(A) State the fundamental law from which this is derived.
(B) Explain how Kirchhoff's Voltage Law validates conservation of energy.
(II) How does the balancing condition of a Wheatstone bridge get affected if galvanometer and cell are interchanged?
✅ Answer & Solution
(I)(A) This is Kirchhoff's Current Law (KCL): $\sum I = 0$ at a junction.
Based on conservation of charge.
(I)(B) KVL states $\sum V = 0$ around any closed loop, meaning:
$$\sum E = \sum IR$$
Total energy supplied = total energy consumed. This directly validates conservation of energy.
(II) The balancing condition $P/Q = R/S$ is NOT affected. At balance, no current flows through the central branch, so the two nodes are at the same potential. Interchanging galvanometer and cell only swaps two equi-potential points — null condition remains unchanged.
