Two parallel, long wires carry currents `t_(1) "and" t_(2)` with `t_(1)gtt_(2)`. When the currents are in the same direction, the magnetic field at a point midway between the wires is 10 `mu`T. If the direction of `i_(2)` is reversed, the field becomes 30 `mu`T. Find the ratio `i_(1)i_(2)`.

Options

A. 1
B. 3
C. 2
D. 4

Answer

c

Explanation

`(mu_(0))/(4pi) (2l_(1))/r-(mu_(0))/(4pi) (2l_(2))/r=10 muT`
`(mu_(0)2l_(1))/(4pir) +(mu_(0))/(4pi) (2l_(2))/r=30 muT`
On solving, `l_(1)=20 A ` and `l_(2)=10 A`
So, `l_(1)//l_(2)=2`