Two point charges of +2 μ C each are separated by 1 m in vacuum. The force between them is (take k = 9× 10⁹ N·m²/C²):

Solution

Physics sir · 3 steps

Convert micro to 10⁻⁶ first, then square the charge, and the powers of ten do the rest.

1. Coulomb's law. The force between two point charges q₁ and q₂ at distance r depends on their product and on r².

   F = (k q₁ q₂)/r²

2. Put in numbers. Each charge is 2 μC = 2 × 10⁻⁶ C, so q₁ q₂ = 4 × 10⁻¹² C². With r = 1 m, F = 9 × 10⁹ × 4 × 10⁻¹² = 36 × 10⁻³ N.
3. So. F = 0.036 N, which is option (b). Both charges are positive, so the force is repulsive.

The idea to keep. In Coulomb's law, write every charge in coulombs before you multiply. Then handle the numbers and the powers of ten separately, and check the unit of the option you pick.

Answer from the NTA final answer key. Solution by PrepWiser.