Which of the following statements are correct?
A. Moving charges produce a magnetic field in the surrounding space.
B. An instrument called the current balance is used to measure mechanical force between two parallel conductors.
C. The electron has an intrinsic magnetic moment, which is known as the orbital magnetic moment.
D. Magnetic field of several sources is the vector addition of magnetic field of each individual source.
E. The radius of the circular component of motion is called the radius of the helix.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A, B, D and E Only
(A) Moving charges produce a magnetic field in the surrounding space. — Correct. A moving charge (a current) sets up a magnetic field around it, as Oersted found.
(B) An instrument called the current balance is used to measure mechanical force between two parallel conductors. — Correct. Two parallel currents attract or repel each other, and the current balance measures this force.
(C) The electron has an intrinsic magnetic moment, which is known as the orbital magnetic moment. — Incorrect. The orbital magnetic moment comes from the electron's revolution about the nucleus. The intrinsic magnetic moment is the spin magnetic moment, which the electron has even when it is not revolving.
(D) Magnetic field of several sources is the vector addition of magnetic field of each individual source. — Correct. Magnetic fields obey the principle of superposition.
(E) The radius of the circular component of motion is called the radius of the helix. — Correct. A charge moving at an angle to \( \vec{B} \) goes round a circle while drifting along \( \vec{B} \). The radius of that circle is the radius of the helix, \( r = mv_{\perp}/(qB) \).
NCERT (2026-27):
Introduction – “… Oersted concluded that moving charges or currents produced a magnetic field in the surrounding space.”
Force Between Two Parallel Currents, the Ampere – “… An instrument called the current balance is used to measure this mechanical force.”
Circular Current Loop as a Magnetic Dipole – “… However, elementary particles such as an electron or a proton also carry an intrinsic magnetic moment, not accounted by circulating currents.”
Sources and Fields – “… Experimentally, it is found to obey the principle of superposition: the magnetic field of several sources is the vector addition of magnetic field of each individual source.”
Motion in a Magnetic Field – “… The radius of the circular component of motion is called the radius of the helix.”