20.A solenoid with 500 turns has a current of 4 A. If its length is 0.5 m, what is the magnetic field inside? (B = μ₀ n I, where n = N/L, μ₀ = 4π × 10⁻⁷ Tm/A) A) 2.5 × 10⁻³ T 😥 B) 4π × 10⁻³ T 👍🏻 C) 5 × 10⁻³ T 😮 D) 6.28 × 10⁻³ T ❤️