Potentiometer + Wheatstone Bridge
Current Electricity
42
JEE Qs
5%
Hard
60
min
Master the null deflection principle for both instruments and practice identifying effective circuit components to correctly apply formulas and analyze complex configurations.
🧮 Key Formulas
✅ Key Points for JEE
- 1A Wheatstone Bridge is balanced when the ratio of resistances in adjacent arms is equal, leading to zero current through the galvanometer and thus zero potential difference across its terminals.
- 2Potentiometer works on the principle that for a uniform wire carrying a constant current, the potential drop across any segment is directly proportional to its length (uniform potential gradient).
- 3The potentiometer is a null deflection instrument, meaning it draws no current from the unknown EMF source at the balance point, providing highly accurate measurements.
- 4The potential gradient of the potentiometer wire must be less than the EMF of the cell being measured, otherwise, a null point cannot be obtained.
- 5Polarity is crucial in potentiometer circuits; the positive terminals of all cells (driver and unknown) must be connected to the same end of the potentiometer wire.
⚠️ Common Mistakes
- ✕Incorrectly identifying the arms (P, Q, R, S) in a Wheatstone bridge, especially when the circuit is drawn in a non-standard configuration.
- ✕Calculating potential gradient incorrectly by using the full EMF of the driver cell instead of the actual potential drop across the potentiometer wire.
- ✕Forgetting to consider the internal resistance of the driver cell or any series resistance in the primary circuit when calculating the primary current and potential gradient.
- ✕Not ensuring that the EMF of the primary driver cell is greater than the EMF of the secondary cell being measured (essential for obtaining a balance point).
- ✕Incorrectly connecting the polarities of the cells in the potentiometer circuit, leading to no null point or incorrect readings.
📝 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