The magnitude of the magnetic field at a distance 'R' from a long, straight wire carrying a current 'I' is equal to ____________. ( 'µ₀' is permeability of free space) 

CONCEPT: 

The magnetic field at point P due to a straight conductor is given by:

B = \(μ_0 I \over{2\pi d}\)

where B is the magnetic field at point P, μ0 permeability of the medium I is the current in the wire and d is the distance from the wire to that point.

EXPLANATION:

Here d = R

At distance R from an infinitely long straight current-carrying conductor, the magnetic field is:

B = \(μ_0 I \over{2\pi R}\)

The correct answer is option 3.