A cylindrical conductor of diameter ( 0.1 ~mm ) carries a current of ( 90 ~mA ). The current density (in ( . Am ⁻² ) ) is ( ( 3) )

Step-by-step solution

Diameter of the wire ( d=0.1 ~mm =10⁻⁴ ~m ² ) Cross-sectional area of the wire ( A= d² 4 ) ( A= 3 (10⁻⁴ )² 4 =0.75 10⁻⁸ ~m ² ) Current flowing through the wire ( I=90 ~mA =90 10⁻³ ~A ) Thus current density ( J= I A ) ( J= 90 10⁻³ 0.75 10⁻⁸ =1.2 10⁷ Am ⁻² )