Question

Explain how Ampere’s law is useful in different situations.

Answer 1

1. Magnetic field due to a long straight current-carrying conductor: By choosing a circular Amperian loop around the wire,
   B = \[\frac{\mu_0 I}{2\pi r}\]
2. Magnetic field inside a long solenoid: Ampere’s law gives
   B = μ₀nI
   where n is the number of turns per unit length.
3. Magnetic field inside a toroid: For a toroid having N turns,
   B = [\frac{\mu_0 NI}{2\pi r}\]

Thus, Ampere’s law provides a simple method for calculating the magnetic field when the current distribution has suitable cylindrical or circular symmetry.