The figure shows an end view of two long, parallel wires perpendicular to the xy plane, one at (0, a) and one at (0, -a), each carrying currrent I = 25.0 A, but out of the page at (0, a) and into the page at (0, -a). a) Find an expression for the magnetic field on the x axis, magnitude and direction, in terms of x and given quantities, using a=5.00 cm. b) At what value of x is the magnitude of! B the greatest? c) What is an approximate expression forB when x >> a? 两电流一个往+Z方向,一个往-Z方向 (a)我算的问题请问积分是由z=负无限到正无限吗? 因为它的改变在x但对z做积分感觉完全没有影响呀 那後两题不就跟x没关系这它这样问好像怪怪得Q_Q 能否有大大可以给我指点一下 谢谢^^ --

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