The Faraday (polarization) rotation of a radio wave of frequency 
is given by:
where the various symbols have their usual meanings.
The position angle of polarization of the radio source Taurus A is 
at a
wavelength of 30cm and 
at 5cm. Taking 
as the mean
longitudinal component of magnetic field and 
as the mean electron
concentration along the path, estimate the distance to Taurus A.
SOLUTION:
Put 
where 
is the wavelength (in metres).
Using mean values to replace the integral by a product:
where R is the distance to Taurus A.
Now:
From the data given:
In astronomical language:
