Practice portal › Electric Charge and Properties › Electric Field of Point Charges

A charge 10⁻⁹ C is located at the origin of a Cartesian co-ordinate system and another charge Q at (2,0,0) m. If the Y-component of the electric field at (3,1,1) m is zero, the value of charge Q is _____ C.

Asked in GUJCET 2013 · Field of discrete charges

Answer: (2) -0.1424×10⁻⁹

Step-by-step solution

Given: q₁=10⁻⁹ C at (0,0,0); Q at (2,0,0); field point P(3,1,1).

Idea: the field of a point charge is ⃗E=(kq ⃗r)/(r³), with ⃗r drawn from the charge to P, so its y-component is (kq y)/(r³).

From q₁: ⃗r₁=(3,1,1), r₁=√11, so E_1y=(k(10⁻⁹)(1))/(11^3/2)

From Q: ⃗r₂=(1,1,1), r₂=√3, so E_2y=(kQ(1))/(3^3/2)

Set E_1y+E_2y=0: (10⁻⁹)/(11^3/2)+Q/(3^3/2)=0

Q=-10⁻⁹(3/(11))^3/2=-10⁻⁹×0.1424

Q=-0.1424×10⁻⁹ C

Why the other options are wrong

More Electric Field of Point Charges questionsAll Electric Field of Point Charges questions →

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.

Practise this with a timer