3.1 Electrostatics

• Origin of charge; the law of electrostatics
• Methods of charging: friction, contact and induction
• The leaf electroscope: parts, charging, discharging and uses
• Charge distribution on conductors of various shapes
• Electric field patterns; force between charges
• Applications of electrostatics

• explain the origin of charges in a material
• describe methods of charging a conductor
• illustrate charge distribution on conductors of various shapes
• explain the functions of the various parts of an electroscope
• illustrate the charging of an electroscope
• appreciate the uses of an electroscope and applications of static charges in day-to-day life

“Why does a plastic comb pick up small pieces of paper after being rubbed on hair?”

“Why is a lightning arrestor pointed rather than rounded?”

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1. Charge, and how things become charged
   40 min · 2 practice tasks · quiz
   Where charge comes from, three ways to move it, and the instrument that detects it.
2. Charge distribution, fields and applications
   40 min · 2 practice tasks · quiz
   Why charge crowds at a point, and how that single fact explains lightning conductors and photocopiers.
3. Where electric charge comes from
   40 min · 1 practice tasks · quiz
   Atoms are neutral until electrons move; a positive body has lost electrons, and charge is conserved.
4. The law of electrostatics
   40 min · 1 practice tasks · quiz
   Suspend a charged rod and test unknowns: like charges repel, unlike charges attract, and repulsion is the conclusive test.
5. Charging by friction
   40 min · 1 practice tasks · quiz
   Rubbing two insulators transfers electrons; which way they go depends on the materials, and a hand-held metal rod will not keep the charge.
6. Charging by contact and by induction
   40 min · 1 practice tasks · quiz
   Touching shares the same sign; induction, with the earth removed first, leaves the opposite sign and a stronger charge.
7. Building a leaf electroscope
   40 min · 1 practice tasks · quiz
   Make a working electroscope from a jar, a nail and aluminium foil, then name the job of each part.
8. Charging, discharging and using an electroscope
   40 min · 1 practice tasks · quiz
   Charge by contact or induction, discharge by earthing, then use the leaf to test presence, sign and whether a material conducts.
9. Electric fields and field patterns
   40 min · 1 practice tasks · quiz
   An electric field is a region where a charge feels a force; field lines run from positive to negative, never cross, and show a uniform field between parallel plates.
10. Electrostatics in Kenyan life
    40 min · 1 practice tasks · quiz
    Lightning conductors, fuel tankers, photocopiers, spray guns and static hazards: action at a point and attraction of opposite charges, applied where you live.