Question

A wire carrying a current of 1 A flows East → West in a region where the horizontal component of Earth's magnetic field is B = 3.0 × 10⁻⁵ T directed South → North. The force per unit length on the wire is:

Options

• \[f = 1.5 \times 10^{-5}\ \text{N/m}\]

• \[f = 3 \times 10^{-5}\ \text{N/m}\]

• \[f = 0\ \text{N/m}\]

• \[f = 2 \times 10^{-7}\ \text{N/m}\]

Answer 1

East–West is perpendicular to South–North, so θ = 90°. Using f = IB sin θ = 1 × 3 × 10⁻⁵ × sin 90° = 3 × 10⁻⁵ N/m. This force is larger than 2 × 10⁻⁷ N/m, the value used to define the ampere.