Electricity Chapter 17

1
ElectricityChapter 17
2
Chapter 17- Electric Charge

• The two different kinds of Electric charges are
  positive and negative
• Like charges repel unlike charges attract
• Protons and neutrons are relatively fixed in the
  nucleus of the atom but electrons are easily
  transferred from one atom to another.

3
Chapter 17- Electric Charge

• All charge is a result of the movement of
  electrons.
• (Chemistry Review)
• All atoms begin as neutral- with no charge.
• If you take away negative electrons then the atom
  has a positive charge.
• If you add negative electrons then the atom
  becomes negatively charged.
• All atoms with a charge are called ions.

4
Chapter 17- Electric Charge

• What causes the electrons to move?
• Friction! When objects rub together electrons are
  moved from one object to the other.
• This causes one object to be positively charged
  and the other to be negatively charged and the
  process is called charge by contact.

5
Chapter 17- Electric Charge
6
Chapter 17- Electric Charge

• The fundamental unit of charge, e, has been
  determined to be 1.6 X 10-19 coulombs
• C (coulomb) is the SI unit of electric charge
• 1.0 C contains 6.2 X 1018 electrons

7
Chapter 17- Electric Charge

• Materials in which electric charges move freely
  are called conductors.
• Ex Copper, Aluminum, most metals
• Materials in which electric charges do not move
  freely are called insulators.
• Ex Wood, glass, styrofoam
• Semiconductors are materials between conductors
  and insulators.
• Ex silicon, germanium

8
Chapter 17- Electric Charge

• Grounding is when a conductor is connected to the
  Earth by another conducting object such as copper
  wire. Many times it is a safety precaution in
  electrical devices.

9
Grounding
10

• Induction is the process of charging a conductor
  by bringing it near another charged object and
  grounding the conductor.

11
Chapter 17- Electric Force

• Electric Force two or more charged objects near
  one another may experience motion either toward
  or away from each other because each object
  exerts a force on the other objects.
• Electric force is an example of a field force (a
  force which does not require physical contact to
  act).

12
Chapter 17- Electric Force

• Coulombs Law
• Felectric kC(q1q2/r2)
• Electric force Coulomb constant X (charge
  1)(charge 2) / (distance)2
• Coulomb constant in SI units
• kC 8.99 X 109 Nm2/C2

13
Electric Charge (on pg 630)
Particle Charge (C) Mass (kg)
Electron -1.60 x 10-19 C 9.109 x 10-31 kg
Proton 1.60 x 10-19 C 1.673 x 10-27 kg
Neutron 0 1.675 x 10-27 kg
14
Example

• The electron and proton of a hydrogen atom are
  separated, on average, by a distance of about 5.3
  x 10-11 m. A.) Find the magnitudes of the
  electric force and B.) The gravitational force
  that each particle exerts on the other.

• Given
• r 5.3 x10-11m
• kc 8.99 x109 Nm2/C2
• qe -1.60 x 10-19 C
• qp 1.60 x 10-19 C
• me 9.109 x 10-31 kg
• mp 1.673 x 10-27 kg
• G 6.67 x10-11 Nm2/kg2

15
Example (magnitude of electrical field force)

• Felectric kc((qeqp)/r2)
• Because we are finding the magnitude of electric
  field force (scalar) we can disregard the sign of
  the charges and simplify.
• Felectric kc((q2)/r2)
• F (8.99 x109 Nm2/C2)(1.60 x 10-19C)2
• (5.3
  x10-11m)2
• Felectric 8.2 x 10-8 N

16
Example (magnitude of gravitational force)

• Given r 5.3 x10-11m me 9.109 x 10-31 kg mp
  1.673 x 10-27 kg G 6.67 x10-11 Nm2/kg2
• Fg G(memp)/r2
• Fg (6.67 x10-11 Nm2/kg2)(9.109 x10-31kg)(1.673
  x10-27kg)
• (5.3 x10-11m)2
• Fg 3.6 x 10-47 N

17
Chapter 17- Electric Field

• Electric field a region in space around a
  charged object in which a stationary charged
  object experiences an electric force because of
  its charge.
• No contact needs to take place for this to occur