根据F=BIL得,B= F IL = 4×10?3 2×0.02 =0.1T.若电流不变,导线长度减小到1cm,则它受磁场力F=BIL=0.1×2×0.01=2×10-3N.此处的磁感应强度不变,为0.1T.故答案为:0.1T,2×10-3N,0.1T