H) Field Intensity and
Distance
Electric Field Strength and distance animation
1) Spherical point charge
Field intensity varies inversely with the square of distance
Double distance from charge,
the field intensity ....
is quartered
2. Charged Rod - the field intensity varies inversely with distance
If the distance to the rod is reduced to 1/3 its original distance, the electric field intensity ...
would be 3 times greater
I.) Electric Potential - work needed or energy acquired when a positive charge is moved from infinity to a certain point in an electric field.
II) Potential Difference (Voltage) potential energy difference between 2 points in an electric field per unit of charge
A) Potential Difference, Energy and Work
As a charge moves through an electric field it gains PE or KE
KE goes up...
When "Opposites" move
closer
"Likes" separated
PE goes up...
When 'Likes' move
closer
'Opposites' separated
1) Equation #1
| V= | W | (Joules) |
| q | (Coulombs) |
W = work done against field or energy acquired working with field (Joules or eV)
eV = electronVolts
(small energy unit)
q
- amount of charge moving through field (Coulombs)
V
- Potential Difference (volts)
Ex) It takes 6 Joules of work to move 2 Coulombs of charge between 2 points in an electric field. What is the potential energy difference (voltage) between these 2 points?
Ex) It takes 6 Joules of work to move 2 coulombs of charge between 2 points in an electric field. What is the potential energy difference (voltage) between these 2 points?
| V= | W | (Joules) |
| q | (Coulombs) |
| V = | 6 Joules |
| 2 Coulombs |
V = 3 Volts or J/C
2) Potential
difference (V) #2
| V= | W | (eV) |
| q | (elementary charges) |
(not on reference)
W = work done against field
or energy acquired working with field
(Electronvolts = Ev)
Electronvolt – small energy unit = 1.6 X 10-19 J
q - amount of
charge moving through field (# elementary charges)
V - Potential Difference
(volts)
Ex) It takes 10 eV to move 2 elementary charges from one point to another in an electric field. Find the potential difference between these points.
Ex) It takes 10 eV to move 2 elementary charges from one point to another in an electric field. Find the potential difference between these points.
| V= | W | (eV) |
| q | (elementary charges) |
| V= | 10 eV |
| 2 elementary charges |
V= 5 Volts
Ex) +2 elementary charges acquire 16 joules of energy when they move between 2 points in an electric field. What is the potential difference (voltage) between these two points in the field?
Ex) +2 elementary charges acquire 16 joules of energy when they move between 2 points in an electric field. What is the potential difference (voltage) between these two points in the field?
Units don't match!!!
elementary charges, eV Joules/Coulombs
+2 elementary charges=
3.2 x 10-19 C
| V= | W | (Joules) |
| q | (Coulombs) |
| V= | 16 J |
| 3.2 x 10-19 C |
V = 5.0 x 1019 Volts or J/C
| Ex) If 4.8 x 10-17 joules of work is required to move an electron between 2 points in an electric field, what is the electric potential difference between these points? | |
|
|
|
| a)3.0 x 102 V | b)4.8 x 10-17 V |
| c) 1.6 x 10-19 V | d) 4.8 x 102 V |
| If 4.8 x 10-17 joule of work is required to move an electron between 2 points in an electric field, what is the electric potential difference between these points? | |
|
|
|
| a)3.0 x 102 V | b)4.8 x 10-17 V |
| c) 1.6 x 10-19 V | d) 4.8 x 102 V |
W = 4.8 x 10-17 joule
V = ?
q = ????????
Hint: The charge in this problem is an electron
q = 1.6 x 10-19
c
Millikan Experiment 1911
Millikan studied charges on oil
drops in a uniform electric field. He suspended the oil drops in
the electric fields and was able to discover:
1) elementary charge
= 1.6 x 10-19 C
2) that all the charges in nature must be a whole number multiple of 1.6 X 10-19 C
Review
Conduction and Induction - St. Mary's H.S.
Why does a charged balloon stick to a wall?
- St. Mary's H.S.
Conservation of Charge - St. Mary's H.S.