Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): At large distances, a circular loop carrying a steady current behaves like a magnetic dipole.
Reason (R): At large distances, the magnetic field of the loop on its axis and in its plane has the form of the field of an electric dipole, with \(m\) in place of \(p_e\) and \(\mu_0\) in place of \(1/\varepsilon_0\).
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are correct and (R) is the correct explanation of (A).
Assertion (A) At large distances, a circular loop carrying a steady current behaves like a magnetic dipole. — True. A plane current loop acts as a magnetic dipole of moment \(m=IA\).
Reason (R) At large distances, the magnetic field of the loop on its axis and in its plane has the form of the field of an electric dipole, with \(m\) in place of \(p_e\) and \(\mu_0\) in place of \(1/\varepsilon_0\). — True. For \(x\gg R\), the field on the axis is \(B\simeq\mu_0 2m/4\pi x^3\) and the field in the plane is \(B\simeq\mu_0 m/4\pi x^3\). For an electric dipole, the fields on the axis and on the perpendicular bisector are \(2p_e/4\pi\varepsilon_0x^3\) and \(p_e/4\pi\varepsilon_0x^3\).
Why Reason (R) explains Assertion (A)?
Both the axial field and the in-plane field of the loop match the fields of an electric dipole after this change of symbols.
So, far from the loop, its whole field is a dipole field. This is the reason the loop is called a magnetic dipole.
NCERT (2026-27):
Circular current loop as a magnetic dipole – “We have shown that a current loop (i) produces a magnetic field … and behaves like a magnetic dipole at large distances, and (ii) is subject to torque like a magnetic needle.”
Circular current loop as a magnetic dipole – “… The expression of Eq. [4.25(a)] is very similar to an expression obtained earlier for the electric field of a dipole.”
\( B\simeq\frac{\mu_0}{4\pi}\,\frac{2m}{x^{3}} \qquad [4.25(a)] \)
Circular current loop as a magnetic dipole – “It can be shown that the above analogy can be carried further. We had found in Chapter 1 that the electric field on the perpendicular bisector of the dipole is given by …”
\( E\simeq\frac{p_e}{4\pi\varepsilon_0x^{3}} \)
“… we obtain the result for B for a point in the plane of the loop at a distance x from the centre. For x >>R,”
\( B\simeq\frac{\mu_0}{4\pi}\,\frac{m}{x^{3}} \)\( \qquad [4.25(b)] \)