Identify the correct statements among the following.
A. The torque acting on a planar current loop in a magnetic field changes when its shape is changed without changing its area.
B. Two parallel wires carrying currents in opposite directions attract each other.
C. An ideal ammeter has zero resistance and an ideal voltmeter has infinite resistance.
D. A galvanometer can be converted into a voltmeter by connecting a high resistance in series.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C and D only
(A) The torque acting on a planar current loop in a magnetic field changes when its shape is changed without changing its area. — Incorrect. The torque is \( \tau = NIAB\sin\theta \); it depends on the area of the loop through the magnetic moment \( m = NIA \), not on its shape.
(B) Two parallel wires carrying currents in opposite directions attract each other. — Incorrect. Like (parallel) currents attract; opposite (antiparallel) currents repel.
(C) An ideal ammeter has zero resistance and an ideal voltmeter has infinite resistance. — Correct. An ammeter goes in series and must not change the current; a voltmeter goes in parallel and must draw no current.
(D) A galvanometer can be converted into a voltmeter by connecting a high resistance in series. — Correct. The series resistance limits the current to the galvanometer's full-scale value at the largest voltage to be measured.
Note: A similar question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 2).
NCERT (2026-27):
Circular Current Loop as a Magnetic Dipole – “… The results obtained above can be shown to apply to any planar loop: a planar current loop is equivalent to a magnetic dipole of dipole moment m = I A, which is the analogue of electric dipole moment p.”
Summary – “… 9. Parallel currents attract and anti-parallel currents repel.”
Summary – “… 11. A moving coil galvanometer can be converted into a ammeter by introducing a shunt resistance rs, of small value in parallel. It can be converted into a voltmeter by introducing a resistance of a large value in series.”