A current of 2A is maintained in a long straight conductor placed in air. Calculate the magnitude of the magnetic field at a distance of 2 m from the conductor.
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( 2\times10^{-7}\,\mathrm{T} \)
The magnetic field of a long straight current, from the Biot-Savart law (or Ampere's circuital law), is
\( \displaystyle B = \frac{\mu_0 I}{2\pi r} \)
\( \mu_0 = 4\pi\times10^{-7}\,\mathrm{T\,m\,A^{-1}} \)
\( I = 2\,\mathrm{A} \)
\( r = 2\,\mathrm{m} \)
\( \displaystyle B = \frac{4\pi\times10^{-7} \times 2}{2\pi \times 2}\,\mathrm{T} = 2\times10^{-7}\,\mathrm{T} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
