Exams › JEE Main › Physics

A square has a charge Q at each pair of diagonally opposite vertices, and a charge q at the remaining two vertices. If the resultant electrostatic force on any one of the charges Q is zero, what is the value of Q/q?

1. −1
2. 1
3. −1/√2
4. −2√2

Correct answer: −2√2

Solution

For charge Q at a corner: the two q charges at the adjacent corners (distance L) give a resultant sqrt(2)*kQq/L^2 along the diagonal, and the opposite Q (distance L*sqrt(2)) gives kQ^2/(2L^2). Setting the net to zero: sqrt(2)*q + Q/2 = 0 -> Q/q = -2*sqrt(2).

Related JEE Main Physics questions

• What is the SI unit of the permittivity of free space, ε₀?
• What is the SI unit used for electric flux?
• A constant electric field E is directed along the positive x-axis. If a charge of 0.5 C is displaced by 2 m along a line inclined at 60° to the x-axis, and the work done in this process is 10 J, what is the magnitude of the electric field?
• An electric dipole is located at the origin O along the x-axis. A point P lies 20 cm from O, and the line OP makes an angle π/3 with the x-axis. If the electric field at P is inclined at an angle θ to the x-axis, what is θ?
• A uniformly charged semicircular wire has radius a and linear charge density λ. The magnitude of the electric field at the centre of the semicircle is
• A point Q is located on the perpendicular bisector of an electric dipole whose dipole moment is p. If Q is at a distance r from the dipole and r is much greater than the dipole size, the electric field at Q varies as

⚔️ Practice JEE Main Physics free + battle 1v1 →