Which are the correct statements from given below:
A. Kirchhoff's junction rule is based on conservation of charge
B. Current is a vector quantity.
C. Current density is a vector quantity.
D. Resistance doesn't depend on dimension of conductor.
E. Resistivity depends on temperature.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A, C, E Only
The statements test the basic quantities of current electricity: current, current density, resistance and resistivity.
(A) Kirchhoff's junction rule is based on conservation of charge — Correct. Charge does not pile up at a junction, so the current flowing in equals the current flowing out; this is conservation of charge.
(B) Current is a vector quantity. — Incorrect. Current has a direction along the wire, but currents do not add by the vector law (at a junction they add as numbers), so current is a scalar.
(C) Current density is a vector quantity. — Correct. Current density \( \vec{j} \) points along the flow of positive charge at each point, and \( I = \vec{j}\cdot\vec{A} \).
(D) Resistance doesn't depend on dimension of conductor. — Incorrect. \( R = \rho l/A \), so resistance depends on the length and the area of cross-section.
(E) Resistivity depends on temperature. — Correct. For a metal, \( \rho_T = \rho_0[1 + \alpha(T - T_0)] \); resistivity depends on the material and its temperature, not on its dimensions.
NCERT (2026-27):
Points to Ponder – “… 6. Kirchhoff’s junction rule is based on conservation of charge and the outgoing currents add up and are equal to incoming current at a junction.”
Ohm’s Law – “… The current density, (which we have defined as the current through unit area normal to the current) is also directed along E, and is also a vector \( \mathbf{j}\ (\equiv j\,\mathbf{E}/E) \).”
Temperature Dependence of Resistivity – “The resistivity of a material is found to be dependent on the temperature.”