A straight wire carrying a current of 10 A produces a magnetic field at a point 5.0 cm away from the wire. The value of the field is

medium MCQ 3 marks Class 12 · Physics · Magnetism and Matter

Answer

4.0×10⁻⁵ T

The correct answer is 4.0×10⁻⁵ T — Round to one significant figure: $4.0 \times 1 0^{- 5}; T$ .

Step-by-step solution

Identify the formula for the magnetic field due to an infinite straight wire: $B = \frac{m u _{0} I}{2 p i r}$ .
Insert the given values: $I = 10; A$ , $r = 0.05; m$ , $μ_{0} = 4 π \times 1 0^{- 7}; T\cdotm/A$ .
Compute the numerator: $μ_{0} I = (4 π \times 1 0^{- 7}) (10) = 4 π \times 1 0^{- 6}; T\cdotm$ .
Compute the denominator: $2 π r = 2 π (0.05) = 0.314; m$ .
Divide: $B = \frac{4 π \times 1 0 ^{- 6}}{0.314} = 4.04 \times 1 0^{- 5}; T$ .
Round to one significant figure: $4.0 \times 1 0^{- 5}; T$ .

Common mistake: Using

r

instead of

2 p i r

in the denominator

Concept tested: Biot–Savart law for straight wire

Published 10 September 2026 · Last updated 16 September 2026 · How this solution was prepared and checked