Kirchhoff's Laws — KCL, KVL, complex networks
Current Electricity
19
JEE Qs
8%
Hard
75
min
Master a consistent sign convention for potential changes in KVL and diligently apply it to avoid common calculation errors.
🧮 Key Formulas
✅ Key Points for JEE
- 1KCL is based on the conservation of electric charge, stating that the algebraic sum of currents at any junction (node) in a network is zero.
- 2KVL is based on the conservation of energy, stating that the algebraic sum of potential differences around any closed loop in a network is zero.
- 3For KVL, consistently apply a sign convention: moving in the direction of current across a resistor, potential drops (-IR); moving against current, potential rises (+IR). For a cell, moving from negative to positive terminal, potential rises (+E); positive to negative, potential drops (-E).
- 4Choose independent equations: For 'N' junctions, there are (N-1) independent KCL equations. Select a sufficient number of independent KVL loops to include all unknown currents/variables.
- 5Assume arbitrary directions for unknown currents; if a calculated current value is negative, its actual direction is opposite to the assumed one.
⚠️ Common Mistakes
- ✕Sign errors in KVL equations, especially when traversing resistors or EMF sources against the assumed current direction or terminal polarity.
- ✕Not identifying the correct number of independent KCL junctions or KVL loops, leading to redundant equations or an insufficient system to solve.
- ✕Incorrectly applying KCL by failing to account for all currents entering or leaving a specific junction.
- ✕Ignoring the internal resistance of cells or batteries when given, which acts as a series resistor in the circuit.
📝 Practice Questions
See allQ47.The value of current I in the electrical circuit as given below, when potential at A is equal to the potential at B, will be ____ A.
Q27.Given below are two statements : Statement-I : The equivalent emf of two nonideal batteries connected in parallel is smaller than either of the two emfs. Statement-II : The equivalent internal resistance of two nonideal batteries connected in parallel is smaller than the internal resistance of either of the two batteries. In the light of the above statements, choose the correct answer from the options given below. (1) Both Statement-I and Statement-II are false (2) Statement-I is false but Statement-II is true (3) Both Statement-I and Statement-II are true (4) Statement-I is true but Statement-II is false
Q34. Sliding contact of a potentiometer is in the middle of the potentiometer wire having resistance Rp = 1Ω as shown in the figure. An external resistance of Re = 2Ω is connected via the sliding contact. The electric current in the circuit is : (1) 0.9 A (2) 1.35 A (3) 0.3 A (4) 1.0 A 2025 (22 Jan Shift 1) JEE Main Previous Year Paper
Q45.Which of the following resistivity ( ρ ) v/s temperature (T) curves is most suitable to be used in wire bound standard resistors? (1) (2) (3) (4)
Q47.The net current flowing in the given circuit is_______ A.
Q30.Refer to the circuit diagram given in the figure. which of the following observations are correct? A. Total resistance of circuit is 6Ω B. Current in Ammeter is 1 A C. Potential across AB is 4 Volts. D. Potential across 2025 (23 Jan Shift 1) JEE Main Previous Year Paper CD is 4 Volts E. Total resistance of the circuit is 8Ω. Choose the correct answer from the options given below: (1) A, B and D Only (2) A, B and C Only (3) A, C and D Only (4) B, C and E Only
NCERT Chapters
- Class 12 Physics Ch 3: Current Electricity