A solenoid has core of a material with relative permeability 400. The winding of the solenoid are insulated from the core and carry a current of 2 ampere. If the number of turns is 1000 per meter, what is magnetic flux density inside the core?

1.0 T

$ B = \mu nI = \mu_0 \mu_r nI = 4\pi \times 10^{-7} \times 400\times 1000\times 2= 1.0T$