Answer : Option C) 2.5 units
Explanation : For calculating the strength of a unknown magnetic field in comparison with the given magnetic field we can use the magnetic formula as;
[tex] \frac{ S_{1}}{S_{2}} = \frac{ (D_{1}^{2}) }{(D_{2}^{2})} .[/tex]
On substituting the values we get;
[tex] \frac{10}{x} = \frac{4^{2}}{2^{2}} [/tex] ;
On solving we get the magnetic B field strength as 2.5 units
