1)

The figure shows the circular coil carrying current l kept very close but not touching at a point  A on a straight conductor carrying the same current l. The magnitude of magnetic induction  at the centre of the circular coil will be 

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A) μ0l2r(1+1π)

B) μ0l2πr

C) μ0l2r

D) zero

E) None of these

Answer:

Option E

Explanation:

 Magnetic  induction at the centre of circular current carrying loop.

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B1=μ0i2r              (downward direction )

 Magnetic induction at the centre O due to straight  wire,

B2=μ02πir   (upward direction)

 Net magnetic induction at O,

 B=B1B2=μ0i2rμ02π.ir

 =μ0i2r[11π]  [ downward direction]

 Hence, there are no option correct.