JEE Main 2024 Physics question
A 2A current carrying straight metal wire of resistance 1Ω, resistivity 2 × 10 Ωm, area of cross –section 10 mm and mass 500 g is suspended horizontally in mid air by applying a uniform magnetic field . The magnitude of B is……………… × 10 T (given, g = 10 m/s)
Answer: 5
Solution
ℓ = RA/ρ = 1 × 10⁻⁵/(2 × 10⁻⁶) = 5 m; BIℓ = mg ⇒ B = 5/(2 × 5) = 0.5 T.