Choose the correct statements from following:
A. Resistivity of a conductor increases with increase in its length.
B. When a small resistor is connected in parallel across a galvanometer, it is converted into ammeter.
C. Current density is a vector quantity.
D. Potentiometer is used to measure the electric current.
E. Kirchhoff's junction rule is based on the conservation of charge.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → B, C & E only
A. Resistivity of a conductor increases with increase in its length — Incorrect. Resistivity depends on the material and its temperature, not on the dimensions. It is the resistance, \( R = \rho l/A \), that increases with length.
B. When a small resistor is connected in parallel across a galvanometer, it is converted into ammeter — Correct. The small shunt resistance carries most of the current, so the combination has a small resistance and can be put in series to read large currents.
C. Current density is a vector quantity — Correct. It has a magnitude (current per unit area) and a direction, \( \vec{j} \), along the direction of the current.
D. Potentiometer is used to measure the electric current — Incorrect. A potentiometer measures potential difference and compares emfs; it does not measure current directly.
E. Kirchhoff’s junction rule is based on the conservation of charge — Correct. Charge cannot pile up at a junction, so the current entering equals the current leaving it.
NCERT (2026-27):
Summary – “… 4. The resistance R of a conductor depends on its length l and cross-sectional area A through the relation,
\( \displaystyle R = \frac{\rho l}{A} \)
where ρ, called resistivity is a property of the material and depends on temperature and pressure.”
Summary – “… 11. A moving coil galvanometer can be converted into a ammeter by introducing a shunt resistance rs, of small value in parallel.”
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 j (≡ j E/E).”
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.”