The ampere is defined as the steady current which, maintained in two l…

Question

The ampere is defined as the steady current which, maintained in two long parallel wires 1 m apart in vacuum, produces a force per metre of length equal to:

Accepted Answer

B. 2 × 10⁻⁷ N m⁻¹

1. Force per unit length: $f = \dfrac{\mu_0 I_a I_b}{2\pi d}$.
2. Set $I_a = I_b = 1$ A and $d = 1$ m.
3. Then $f = \dfrac{4\pi	imes10^{-7}	imes1	imes1}{2\pi	imes1} = 2	imes10^{-7}$.
4. So the defining force is $2	imes10^{-7}$ N per metre of length.
_Source: NCERT Class 12 Physics Ch 4 "Moving Charges and Magnetism", p.156_

Answer

2 × 10⁻⁷ N

Answer

1 × 10⁻⁷ N m⁻¹

Answer

4π × 10⁻⁷ N m⁻¹