Answer-
Mean radius of the Rowland ring is given = 15 cm
Number of turns = 3500
Relative permeability of the core is given by μr = 800
Magnetizing current is given by I = 1.2 A
Magnetic field at the core is given by the relation –
\[B=\frac{{{\mu }_{r}}{{\mu }_{0}}IN}{2\pi r}=\frac{800\times 4\pi \times {{10}^{-7}}\times 1.2\times 3500}{2\pi \times 0.15}\]
\[B=4.48T\]
The magnetic field at the core is 4.48 T.