1. Electricity The Electric Charge The Electron Insulators and Conductors
The Gold-Leaf Electroscope
Redistribution of Charge
Charging by Induction
Coulomb’s Law of Electric Force

2. Electricity
Charge

3. Objectives
Define the nature of electric charge, and describe how objects can obtain a negative or positive charge
Distinguish between insulators, conductors, and semi-conductors
Explain how the gold-leaf electroscope can be used to determine a charge
State and apply Coulomb’s Law

4. Electrostatics Static electricity Unit of charge
Stationary electricity in the form of a electric charge “at rest”
Symbol for charge is “q” or “Q”
Unit of charge
Coulomb
Symbol for coulomb is “C”

5. Elementary Charge Smallest unit of charge
Charge is quantized
Atoms contain elementary charges
Electron (-e) = -1.6 x C
Proton (+e) = 1.6 x C
Neutron (0) = no charge

6. The Electric Charge Neutral objects Charged objects
Number of negative charges equals the number of positive charges
Charge is balanced (equilibrium)
Charged objects
Charge is transferred from one object to another
Charge is separated within an object

7. The Electric Charge
A force of repulsion exists between two substances that are electrified in the same way.
First Law of Electrostatics: Like charges repel and unlike charges attract.

8. The Electron
An object that has an excess of electrons is negatively charged.
An object that has a deficiency of electrons is positively charged.

9. Insulators and Conductors
A conductor is a material through which charges can be easily transferred.
Such as metals, that allow charges to move about freely
Charges spread out over the surface
An insulator is a material that resists the transfer of charge.
Materials through which charges will not move easily
Charges stay where they are placed
A semiconductor is a material that transfers charges better than an insulator but not as well as a conductor.

10. Charging by Conduction
Charging a neutral object by touching it with a charged body
Charges are transferred to the object
Charges spread over all metal surfaces

11. Charging by Induction
A charged body is brought near another object without touching it
Charges are separated in the object
Like charges within the object are forced to move away from a charged body to another part of the object OR
Opposite charges within the object are forced to move toward a charged body leaving like charges in another part of the object

12. Charging by Induction H O Dipole moment of water molecule
Water bends toward positive charge H O

13. Charging by Induction H O Dipole moment of water molecule
Water bends toward negative charge H O

14. The Gold-Leaf Electroscope

15. Redistribution of Charge
When a charged rod is brought close to an uncharged pith ball there is an initial attraction.
No charge is gained or lost during this process--the charge on the neutral body is simply redistributed.

16. Charging by Induction
Charging by induction: The redistribution of charge due to the presence of a nearby charged object.
Charging by induction can be accomplished without any loss of charge from the charging body.

17. Coulomb’s Law Coulomb’s Law
The force of attraction or repulsion between two point charges is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them.
k = 8.99 x 109 N·m2/C2
One coulomb is the charge transferred through any cross-section of a conductor in one second by a constant current of one ampere.
1 C = 6.25 x 1018 electrons

18. Summary of New Terms electrostatics charging electron negative charge
positive charge
ion
induced charge
conductor
insulator
semiconductor
Coulomb’s law
coulomb
microcoulomb
electroscope

19. What is the electrical force on A?
Example
3.0 cm
q = 6 μC
q = 3 μC A B
What is the electrical force on A?

20. Answer