The electric current in a circular coil of two turns produced a magnetic induction of 0.2 T at its centre . The coil is unwounded and then rewounded into circular coil of four turns . If same current flows in the coil , the magnetic induction at the centre of coil now is ?

1 ) The electric current in a circular coil of two turns produced a magnetic induction of 0.2 T at its center . The coil is unwounded and then rewounded into circular coil of four turns . If same current flows in the coil , the magnetic induction at the center of coil now is : -

A ) 0.1 T ,                                                  B ) 0.8 T ,

C ) 2.9 T ,                                                  D ) None of these ,

Correct Answer : -   B ) 0.8 T ,

Solution : -

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2 ) An electron moves at right angle to magnetic field of 1.5 x 10^(-2) tesla with a speed of 6 x 10^7 m / s . If the specific charge of electron is 17 coulomb / kg , the radius of circular path will be : -

A ) 1.5 cm ,                                                B ) 2.35 cm ,      

C ) 3.91 cm ,                                              D ) None of these ,

Correct Answer : -   B ) 2.35 cm ,

Solution : -

For a charge particle moving perpendicular to the field .

Radius : -  r  =  mv / Bq .

Specific charge  =  q / m  =  1.7 x 10 ^ 11  C / kg .

So  ,  r  =  ( 6 x 10 ^ 7 )  /  ( 1.7 x 10^11 x 1.5 x 10^(-2) )  ,

r  =  2.35 x 10 ^ ( -2 ) m  ,

So ,  r = 2.35 cm  ,  Answer .

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