Coulomb's lawAQA A-Level Physics: Mind map

Exam questions on Coulomb's law

1. Two small metal spheres in air carry charges of +3.0 nC and −5.0 nC. Their centres are 4.0 cm apart.
   Calculate the magnitude of the electrostatic force between the spheres. Use $\varepsilon_0 = 8.85 \times 10^{-12}\ \mathrm{F\,m^{-1}}$.2 marks
2. In a hydrogen atom an electron orbits a proton. The mean separation of the particles is 5.3 × 10⁻¹¹ m. A student compares the electrostatic and gravitational forces between them.
   Calculate the ratio of the electrostatic force to the gravitational force between the proton and the electron, and state why the ratio does not depend on their separation. Use $e = 1.60 \times 10^{-19}$ C, $m_e = 9.11 \times 10^{-31}$ kg, $m_p = 1.67 \times 10^{-27}$ kg, $G = 6.67 \times 10^{-11}\ \mathrm{N\,m^2\,kg^{-2}}$ and $\varepsilon_0 = 8.85 \times 10^{-12}\ \mathrm{F\,m^{-1}}$.2 marks
3. A charged metal sphere of radius 2.0 cm carries a charge of +8.0 nC. A small ball carrying −2.0 nC is held in air with its centre 10.0 cm from the centre of the sphere.
   Calculate the magnitude of the electrostatic force between the sphere and the ball. Use $\varepsilon_0 = 8.85 \times 10^{-12}\ \mathrm{F\,m^{-1}}$.3 marks