Two long and parallel straight wires A and B carrying currents of 10.0 A and 5.0 A in the same direction are separated by a distance of 5.0 cm. Estimate the force on a 10 cm section of wire A.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( 2 \times 10^{-5}\,\mathrm{N} \)
The force per unit length between two long parallel currents is given below; it is attractive when the currents are in the same direction. Here \( \mu_0/2\pi = 2\times10^{-7}\,\mathrm{T\,m\,A^{-1}} \).
\( \displaystyle \frac{F}{L} = \frac{\mu_0 I_1 I_2}{2\pi d} \)
\( d = 5.0\,\mathrm{cm} = 0.05\,\mathrm{m} \)
\( L = 10\,\mathrm{cm} = 0.1\,\mathrm{m} \)
\( \displaystyle F = \frac{\mu_0 I_1 I_2}{2\pi d}\,L = \frac{2\times10^{-7} \times 10 \times 5}{0.05} \times 0.1 \)
\( \displaystyle F = 2\times10^{-5}\,\mathrm{N} \)
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 – …
