WEBVTT 00:00:00.500 --> 00:00:03.975 Welcome to GCSE Edexcel Science revision. 00:00:04.125 --> 00:00:07.254 Unit S P 11: Static electricity. 00:00:09.933 --> 00:00:14.808 Rubbing two suitable insulating materials can transfer electrons between them. 00:00:14.958 --> 00:00:24.215 The material gaining electrons becomes negatively charged; the material losing electrons has an equal positive charge if no charge is lost elsewhere. 00:00:26.867 --> 00:00:31.282 Rubbing suitable insulators transfers electrons, not protons. 00:00:31.432 --> 00:00:38.855 An object becomes positive when it has lost electrons (has an electron deficit); no new positive particles are created. 00:00:41.533 --> 00:00:46.771 Charge is conserved: equal and opposite changes do not create net charge from nothing. 00:00:46.921 --> 00:00:56.220 Insulators retain localised charge because charges cannot move freely through the whole material; conductors allow mobile charge to redistribute. 00:00:58.900 --> 00:01:02.235 Like charges repel and unlike charges attract. 00:01:02.385 --> 00:01:10.277 The force is non-contact and acts through an electric field; attraction alone does not prove that two objects carry opposite net charges. 00:01:12.933 --> 00:01:16.630 A charged object can attract a neutral object by induction. 00:01:16.780 --> 00:01:24.276 Charges in the neutral object move or shift slightly (polarisation), making the near side effectively oppositely charged. 00:01:24.426 --> 00:01:28.703 Attraction to the near side is stronger than repulsion from the far side. 00:01:31.367 --> 00:01:36.701 A rubbed balloon can stick to a wall, and a charged comb can pick up small pieces of paper. 00:01:36.851 --> 00:01:41.008 They cause charges in the neutral material to shift slightly (polarise). 00:01:41.158 --> 00:01:44.759 The wall or paper does not need a permanent overall charge. 00:01:47.433 --> 00:01:53.683 A large potential difference can make air conduct and allow a sudden charge transfer, producing a spark. 00:01:53.833 --> 00:02:00.456 Everyday shocks after walking on a carpet arise from a charge imbalance discharged when a conducting path forms. 00:02:03.133 --> 00:02:10.481 Lightning is a large electrical discharge associated with charge separation in clouds and between clouds or ground. 00:02:10.631 --> 00:02:15.793 It transfers charge through ionised air; it is not frictional heating of rain alone. 00:02:18.467 --> 00:02:21.496 Earthing connects an object to Earth through a conductor. 00:02:21.646 --> 00:02:29.751 Electrons can move to Earth from a negatively charged object or from Earth to a positively charged object, reducing the imbalance. 00:02:29.901 --> 00:02:34.252 Electron direction depends on the initial sign of the object's charge. 00:02:38.933 --> 00:02:43.704 During fuel transfer, charge build-up and sparks can ignite flammable vapour. 00:02:43.854 --> 00:02:51.309 Bonding conducting parts and earthing suitable equipment reduce dangerous potential differences and charge accumulation. 00:02:53.967 --> 00:02:59.672 An electrostatic sprayer gives droplets the same charge so they repel one another and spread out. 00:02:59.822 --> 00:03:07.789 Attraction towards an appropriately charged or earthed target can improve coverage and reduce waste; use appropriate safety controls. 00:03:10.467 --> 00:03:18.465 Electrostatic methods can be useful, but evaluate exposure, ignition risks, target coverage and unintended drift in context. 00:03:18.615 --> 00:03:22.281 Charge effects do not remove all problems with an insecticide. 00:03:24.933 --> 00:03:29.533 An electric field is a region where an electric charge experiences a force. 00:03:29.683 --> 00:03:38.823 Field direction is defined as the direction of force on a small positive test charge; a negative charge experiences force in the opposite direction. 00:03:41.500 --> 00:03:48.891 Electric field lines point outwards in all directions from a positive point charge and inwards towards a negative point charge. 00:03:49.041 --> 00:03:54.406 They show the field direction; they are not physical threads or compulsory paths for particles. 00:03:54.556 --> 00:04:01.136 The direction is the force direction for a positive test charge; these are separate isolated-charge diagrams. 00:04:05.800 --> 00:04:08.829 Between large parallel oppositely charged plates, 00:04:08.979 --> 00:04:11.838 the central field is approximately uniform, 00:04:11.988 --> 00:04:17.150 with straight parallel equally spaced lines from the positive plate to the negative plate. 00:04:17.300 --> 00:04:19.465 Near the edges the field curves. 00:04:19.615 --> 00:04:22.685 Edge effects are omitted from this central-region model. 00:04:27.367 --> 00:04:36.047 Closer field-line spacing represents a stronger field; the number and density of drawn lines are a representation, not a count of electrons. 00:04:36.197 --> 00:04:40.523 Lines do not cross because the field has one direction at a given point. 00:04:43.200 --> 00:04:51.562 The field model explains non-contact forces and induction: charges affect nearby charges through the field even when objects do not touch. 00:04:51.712 --> 00:04:55.589 Force direction depends on both field direction and charge sign. 00:04:58.267 --> 00:05:05.007 In simple qualitative diagrams, use arrowheads and plus or minus labels so colour alone is not needed. 00:05:05.157 --> 00:05:09.201 Distinguish conventional field direction from electron motion. 00:05:11.867 --> 00:05:14.202 That completes Static electricity. 00:05:14.352 --> 00:05:17.697 Revisit the notes and test yourself on the revision website.