Download CHAPTER 16-17 • Electric Charge •Insulators vs. Conductors

CHAPTER 16-17
• Electric Charge
•Insulators vs. Conductors
• Induced Charge
•Coulomb’s Law
• Solving Problems Involving Coulomb’s Law and Vectors
• The Electric Field
•Electric Potential Energy
•Potential Difference
The electric charge
• Objects become charged by transferring electrons
• Remove electrons → objects have positive charge
• Add electrons → objects have electrons charge
• Opposite charges Attract
• Like Charges repel
The electric charge
• Electric Charge measured in COULOMBS.
• A typical lightning bolt is only 15 C.
• Charge of electron → 𝑞𝑒 = −1.602 ∗ 10
− 19
𝐶
• Rubbing a balloon on your head will transfer about
CHARGING BY CONDUCTION
Charging By Induction: No Direct contact.
Coulombs Law
Q1, Q2 = Electric Charge\
r = distance between charges
+
r=.25m
5μC
+
-
r=.25m
5μC
5μC +
+F → Charges are repelled
3μC
r=.25m
-
3μC
- 3μC
-F → Charges are attracted
Coulombs Law
• Principle of Superposition
A
+
0.30m
B
C
0.40m
+
4μC
3μC
FAB=
5μC
FAC=
FBC=
FAB
A
FAC
B
FAB
FBC
FBC
FAC
C
Coulombs Law
• Principle of Superposition 2D
A
+
3μC
Find the magnitude and direction of
the Net Force on charge B
0.30m
B
FAB
B
+
4μC
0.40m
5μC
C
FBC
FBC
FAB
The Electric Field
• Area around a charge that exerts a force on other charges
• Field Strength defined as Force per Unit Charge
The Electric Field
The Electric Field
• Field Lines
• The direction of an electric field can be determined based on the
direction a positive charge would move
• WWPCD
WWEKD?
The Electric Field
A
+
3μC
0.40m
0.30m
E=?
B
5μC
The Electric Field
A
6μC
+
Find the magnitude and direction of
the Electric Field at the origin
0.40m
E=?
0.50m
7μC
B
Electric Potential Energy
• Potential Energy = ability of a force to do work.
• Work can be done on an Electric Charge in an Electric Field.
• 𝑊 = 𝐹𝑑 → 𝐸 =
𝐹
𝑞
→ 𝐹 = 𝑞𝐸 → 𝑊 = 𝑞𝐸𝑑 = 𝑃𝐸
𝑃𝐸 = 𝑞𝐸𝑑
Electric Potential / Potential Difference
• Electric potential = Defined as potential energy per unit charge.
• Potential Difference = Work done per unit charge
•𝑉=
𝑃𝐸
𝑞
•𝑉=
𝑃𝐸
𝑞
=
𝑊
𝑞
=
𝑞𝐸𝑑
𝑞
= 𝐽ൗ𝐶 = 𝑉𝑜𝑙𝑡
= 𝐸𝑑
𝑊
𝑉=
= 𝐸𝑑
𝑞
Electric Potential / Potential Difference
• Positive charges move
from High Potential to
Low Potential
• (fall down)
• Negative charges move
from Low Potential to
High Potential
• (fall up)
Electric Potential / Potential Difference
Examples:
• How much work is done moving a 5uC charge from zero potential to
12V of potential?
• How strong is the electric field between to plates 7.0mm apart if the
potential difference between them is 12V?
New unit for electric field →
𝑉 = 𝐸𝑑 → 𝐸 =
𝐸
𝑑
= 𝑉Τ𝑚