1. Two-point charges of + 10 nC and -10 nC in air are separated by a distance of 15 mm. a) Calculate the force acting between the two charges. b) Comment on whether this force can lift a small piece of paper about 2 mm x 2 mm in area. 2. Two-point charges of magnitude +5 uC and +3 uC are 1.5 m apart in a liquid that has a permittivity of 2.3 x 10^ - 11 C^2 N^-1 m^-2. Calculate the force between the point charges. 3. Calculate the electric field strengths in a vacuum a) 1.5 cm from a +10 JC charge b) 2.5 m from a -0.85 mC charge 4. An oxygen nucleus has a charge of +Se. Calculate the electric field strength at a distance of 0.68 nm from the nucleus. 5. Two-point charges, a +25 nC charge X and a + 15 nc charge Y are separated by a distance of 0.5 m. a) Calculate the resultant electric field strength at the midpoint between the charges. b) Calculate the distance from X at which the electric field strength is zero