Eduqas Physics for A Level Year 2: Student Bk

99 2.6 Electrostatic and gravitational fields of force 150 kV m –1 10 cm 20 cm X Y Exercise 2.6 1 The diagram of electric field lines has several (intentional) mistakes. Identify them. The shaded objects are electrical conductors. 2 Diagrams (a) and (b) are of electrical field lines in different regions of space. In each case, draw an equipotential surface (line) through the point P and a second equipotential line which is at a higher potential. (b) P (a) P 3 Two points, X and Y , are positioned as shown in a uniform electric field of intensity 150 kV m −1 . (a) Explain which point is at the higher potential. (b) State the pd between X and Y . (c) A particle with a charge of + 10 μC is released at zero speed from X . Its path takes it subsequently through Y (presumably along a frictionless tube!). Assuming no friction, state its kinetic energy at Y . (d) Calculate the speed a proton would acquire in moving from X to Y . (e) A 7 3 Li nucleus moves on a path that takes it through Y and X . Its kinetic energy at Y is 100 keV . Calculate its speed at X . [You may need to use a data book for the mass and charge of a 7 3 Li nucleus.] 4 A hollow sphere of radius 10 cm carries a positive charge of 1.2 µC . There are no other charges nearby. (a) Describe the distribution of charge. (b) Calculate the electric potential of the sphere and the electric field strength at its outer surface. (c) State the potential and field strength: (i) at a point 20 cm from the centre of the sphere (ii) at the centre of the sphere [One of these requires a trivial calculation.] 5 A small conducting sphere of mass 10 mg touches the outside of the charged sphere in Q4 and acquires a charge of + 10 nC . It is observed to move rapidly away. (a) Explain this observation. (b) Calculate its initial acceleration. (c) Assuming no other significant forces act, calculate its final velocity. 6 Three charges are arranged in a right-angled isosceles triangle. The separation of the −20 µC from each of the other charges is 10 cm . The charges are not free to move. (a) Calculate the electrical potential energy of the arrangement. (b) Calculate the resultant electrical force on each charge due to the other two charges. 10 μ C 10 μ C –20 μ C