For a long wire carrying a current of 10 A, the magnitude of magnetic field at a point 4 cm away from it will be:

$5×10^{-5}T$

The correct answer is Option (4) → $5×10^{-5}T$

Magnetic field (B) at a point near a long, straight current carrying wire is -

$B=\frac{μ_0I}{2πr}$

I (Current through wire) = 10 A

$r$ (Distance from wire) = 4 cm = 0.04 m

$∴B=\frac{4π×10^7×10}{2π×0.04}=5×10^{-5}T$