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D1 Electrostatics
from Physics Workbook for CSEC
by Collins
1 a) When a polythene rod is rubbed with a dry cloth it becomes negatively charged. Explain, in terms of electron flow, why this occurs. b) When a Perspex rod is rubbed with a dry cloth it becomes positively charged. Explain, in terms of electron flow, why this occurs. c) Saishma demonstrates a ‘trick’ to her friends. She rubs a pen against her hair and then uses it to pick up small pieces of paper. Explain how the pen is able to pick up the uncharged pieces of paper. d) A positively charged metal sphere A rests on an insulated stand. A negatively charged metal sphere B rests on an insulated stand. A thick piece of copper wire is used to connect both spheres. A current of 4 μA flows for 2 ms. i) State the direction of electron flow between the two spheres. ii) Calculate the amount of charge that flows between the two spheres. iii) Calculate the number of electrons that were transferred between the two spheres. charge on an electron = –1·6 × 10−19 C
2 a) Explain what is meant by an ‘electric field’. b) Sketch the electric field for EACH of the following: i) an isolated positive charge.