It is known that the uniform section of the magnetic path S = 5cm.^2, the average length is L = 100cm = 1m, the relative permeability of the medium is ur = 1000, the number of turns of the iron core coil is N= 500, the current I=2A, the magnetic flux density B is __T, the magnetic field strength H=___A/m. The magnetic permeability in vacuum is u0, publicly stated as follows. The first empty calculation result is retained to two digits after the decimal point. Integers should not be written in the form of 10.00. Directly 10 can be used. Choose A or B. 第一空计算结果保留到小数点后两位,整数,不要写成10.00的形式,直接10就可以。