14. STATIC ELECTRICITY

14. STATIC ELECTRICITY
Key notes:
1. There are two types of electric charges, i.e. positive and negative charges.
2. Charge is measured in coulombs (C).
3. Like charges repel; unlike charges attract.
4. When an object loses or gains electrons, its becomes charged.
5. An object becomes negatively charged if it gains electrons. It becomes
positively charged if it loses electrons.
6. Electrical conductors allow charges (electrons) to flow easily while electrical
insulators do not.
7. When a positively charged object is earthed, electrons flow from the earth to
the object.
8. When a negatively charged object is earthed, electrons flow from the earth to
the object.
9. When a negatively charged object is earthed, electrons flow from the object to
the earth.
10. Water and human body can conduct charges but they are poor conductors.
11. In electrostatic induction, the charge induced close to the inducing charge is
equal and opposite.
12. To charge a body positively by induction, a negatively charged body is
needed.
13. An uncharged gold leaf electroscope can only determine whether an object is
charged or not. It cannot determine the type of charge on the object.
14. A charged electroscope is used to identify the type of charge in an object, and
to determine whether a material is an insulator or conductor of an electric
charge.
15. Charges building up on an insulated object may cause sparks to occur.
16. To prevent sparks occurring, a