An aeroplane having a wing span of 40 m flies due north at a speed of \( 100\,\mathrm{m\,s^{-1}} \) in magnetic field \( 5 \times 10^{-5}\,\mathrm{T} \) acting vertically downward. The potential difference between the tips of the wings is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 0.2 V
The wings form a conductor of length \( l \) moving through the field, so a motional emf \( \varepsilon = Blv \) appears between the tips. The wings are horizontal (east-west), the velocity is due north and the field is vertical, so \( B \), \( l \) and \( v \) are mutually perpendicular.
\( B = 5\times10^{-5}\,\mathrm{T} \)
\( l = 40\,\mathrm{m} \)
\( v = 100\,\mathrm{m\,s^{-1}} \)
\( \displaystyle \varepsilon = B\,l\,v = 5\times10^{-5} \times 40 \times 100 = 0.2\,\mathrm{V} \)