A coil of `50` turns and `20 cm` diameter is made with a wire of `0.2 mm` diameter and resistivity `2xx10^(-6)Omega cm`.The coil is connected to a source of `EMF`.`20 V` and negligible internal resistance.
(a)Find the current through the coil.
(b)What must be the minimum potential difference across the coil so as to nullify the earth's horizontal magnetic induction `3.14xx10^(-5) tesla` at the centre of the coil.How should the coil be placed to achieve the above result.

Answer

A, B, C, D

Explanation

`L=Nxx2pir-50xx2xxpixx0.1`
`A=pi r^(2)`
`=pixx(0.1xx10^(-3))^(2)`
Resistance `R=(rhoL)/A=(2xx10^(-8)xx50xx2xxpixx0.1)/(pixx10^(-8))=20Omega`
`i=epsilon/R=1A rArr B_(H)=(mu_(0)Ni)/(2r)`