# Teacher’s Notes This sequence of slides is designed to introduce, and explain electrostatic charging by friction, as explained on page 242 in New Physics.

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Teacher’s Notes This sequence of slides is designed to introduce, and explain electrostatic charging by friction, as explained on page 242 in New Physics for You, 2006 & 2011 editions (page 248 in Physics for You, 2001 edition). Note : When you start this PowerPoint if you see a message about “Read-only embedded fonts” then you are recommended to select “Open Read-Only” as this (i) gives a clearer font for those at the back of the room and (ii) ensures that the text-highlighting of key words is correct. On each slide the key points are revealed step by step, at the click of your mouse (or the press of a key such as the space-bar). Before making the next mouse-click you can ask questions of the class or make statements about what is about to be revealed. This should help students to become clearer about the ideas involved. Naturally it pays to have quick practice-run first. To start the slide-show, press function-key F5 (or right-click->Full Screen) (to return to ‘normal view’ press the key). For more (free) PowerPoint presentations, visit www.physics4u.co.uk

Charging by friction New Physics for You, page 242

How insulated objects can be charged by friction, That this is because some charges can move. Learning Objectives You should learn :

Charging by friction The wool and polythene are each ‘uncharged’. What does this mean? In this diagram:

Charging by friction The wool is ‘uncharged’, because… …it has equal amounts of positive and negative charge. Equal numbers of + and − On the wool + − + + − − + − − + − + +−+−−++−+−−+ On the polythene

Charging by friction Equal numbers of + and − on the wool: (Count them!) 7 + 7 − Equal numbers of + and − on the polythene: (Count them!) 3 + 3 − + − + + − − + − − + − + +−+−−++−+−−+

Charging by friction If you rub the wool on the polythene, some electrons ( − ) move from the wool to the polythene. There are now more + than − on the wool: (Count them!) + − + − + − + − + + − − +− − + So now the wool is charged positively, with a surplus of 3 +

Charging by friction What has happened to the polythene? There are now more − than + on the polythene: (Count them!) + − + − + − + − + + − − +− − + So now the polythene is charged negatively, with a surplus of 3 −

Charging by friction Both objects are now equally charged, with opposite charges because electrons − (only) have moved. This is summed up in the diagram on page 242:

Understand what it means when an object is ‘charged’ or ‘uncharged’, Understand how an insulated object becomes charged by rubbing, Understand why the objects have equal but opposite charges, Know that only electrons ( −) can move. Learning Outcomes You should now:

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