Electric Forces and Electric Fields

1
Chapter 15

• Electric Forces and Electric Fields

2
Electric Charges

• Two kinds
• Positive
• Negative -
• Like charges repel
• Unlike charges attract

-

3
Electric Charges

• Charge is Conserved
• Charge is Quantized electron charge (e)
• Unit of Charge - Coulomb (C)
• e 1.60x10-19 C

4
Nature of Matter

• Matter made up of charged particles, positive
  nuclei and negative electrons
• Most matter is neutral, sum of charges zero
• Most often charge transfer is due to movement of
  electrons

5
Insulators and Conductors

• Insulators-do not conduct charge-Glass, rubber,
  paper, plastic
• Conductors- conduct charge Metals
• Semiconductors- intermediate conduction
  properties, important for electronic devices that
  control charge flow- Silicon, germanium

6
Charging by Rubbing
Triboelectic sequence Fur Glass Silk Cotton Wood R
ubber
Positive
negative
Negative charges transferred from glass to silk
7
Charging by conduction
Charged rubber rod transfers electrons to metal
sphere
8
Induced charge (Polarization)

• - - -
• - - -
• - - -

• - -
• - -
• - -

Attraction due to induced charge
9
Charging by induction (polarization)
Ground- sink for electric charge
10
Detecting charge - Electroscope
11
Charging Van de Graaf Generator
Charge accumulates
Spark- charge conduction due to ionization of
atoms.