Practice question

Given: A long wire carries 20 A . At what distance from the wire is the magnetic field 4 × 10⁻⁶T ? ( μ_0 = 4 π × 10⁻⁷T m/A ) These values define the system as per NCERT data. Formula: B = μ_0 I/2 π r, so r = μ_0 I/2 π B. This is standard NCERT relation. Substitution & Calculation: r = frac4 π × 10⁻⁷ × 202 π × 4 × 10⁻⁶= frac8 × 10⁻⁶⁸ × 10⁻⁶= 1 m . Result: The computed value matches expected outcome and confirms correct choice as per NCERT.