Three charges q, $$-$$q and q₀ are placed as shown in figure. The magnitude of the net force on the charge q₀ at point O is $$\left[ {k = {1 \over {(4\pi { \in _0})}}} \right]$$

A + 3.0 nC charge Q is initially at rest at a distance of r₁ = 10 cm from a + 5.0 nC charge q fixed at the origin. The charge Q is moved away from q to a new position at r₂ = 15 cm. In this process work done by the field is

A car battery is charged by a 12 V supply, and energy stored in it is 7.20 $$\times$$ 10⁵ J. The charge passed through the battery is -

A straight conducting rod of length l and mass m is suspended in a horizontal plane by a pair of flexible strings in a magnetic field of magnitude B. To remove the tension in the supporting strings, the magnitude of the current in the wire is