Question

Calculate the charge density for the current density given 20sin x i + ycos z j at the origin.

(a) 20t

(b) 21t

(c) 19t

(d) -20t

The question was posed to me in a job interview.

Enquiry is from Continuity Equation in portion Electric Fields in Material Space of Electromagnetic Theory

Answer 1

Correct option is (b) 21t

Explanation: Using continuity equation, the problem can be solved. Div(J) =

– dρ/dt. Div(J) = 20cos x + cos z. At origin, we get 20cos 0 + cos 0 = 21. To get ρ, on integrating the Div(J) with respect to t, the charge density will be 21t.