1. Warm Up 3
36 The illustration shows the transcription process. What is the main purpose of the structure labeled W?
F Carrying instructions for protein synthesis
G Transforming into a protein
H Replacing damaged DNA
J Passing traits to offspring

2. Electric & Gravitational Fields and Electric Potentials

3. Gravitational vs Electrical Force Discussion
Gravitational Force acts between 2 _____.
Electrical Force acts between 2 _____.
In which direction does the gravitational force act? How about the electrical force?
Does gravity get stronger or weaker from the center of a mass? How about electrical force?
Do these 2 forces seem similar?

4. Gravity and Electricity
Gravitational Force
Electrical Force
Force between 2 masses
Force between 2 charges
Attraction only
Attraction & Repulsion
Weaker over distance
Cause things to orbit
Cause electrons to orbit
G = 6.67 x Nm2/kg2
k = 8.99 x 109 Nm2/C2

5. Force Fields in Physics
Force Fields are just areas with forces.
Gravitational Field – Area where the force of gravity pulls on an object
Electric Field – Area where an electric force can push or pull an object

6. Repulsion or Attraction?
Visualization of an electric field
Polarized thread in oil

7. Attraction or Repulsion?
Line model

8. Force Fields in Physics
Force fields are drawn with lines
The lines represent the direction positive charge would accelerate if placed in the field.
The result is lines start from a positive charge and end at a negative charge

9. Force Fields in Physics
Force fields are drawn with lines
The density of lines represent magnitude

10. Electrical Potential Energy
Think about trying to bring together 2 magnets at their North poles.
How much force does it take for you to bring them together? At the beginning versus when they are really close?

11. Electrical Potential Energy
Electrical Potential Energy – Energy required to keep a charge from moving in an electric field.
Strong field + strong charge + short distance = high Electrical Potential Energy
When the charge is released, that potential energy is transformed to kinetic energy

12. Electric Potential
Electric potential = “electric potential energy”/”charge”
SI unit for Electric Potential is the “volt”, V

13. Misconceptions of the Volt
High Voltage is deadly
Van de Graaff generators can easily generate 50,000 V
High potential energy but very little charge

14. Sample Problem
If 20. J of work is required to move 4.0 C of charge in a uniform electric field, the electric potential will be _____.
A) 80. V
B) 5.0 V
C) 0.0 V
D) 100 V

15. Exit Ticket 2
Consider two charged objects. One carries a charge of 1.8 x10-6 C When the two are separated by a distance of 0.9m, there is a force of 2.7 N between them. What is the charge on the second object?

16. Warm Up 4

17. Electric Potential Energy
Electric Potential Energy (ePE) is due to a charge’s location in an electric field
ePE is the amount of work needed to move a charge to that location
Similar to gravitational potential energy depends on the height of an object
The amount of charge you are moving does not matter

18. Lightning
High Electric Potential is created by friction and air currents in the clouds
Clouds become polarized, usually bottom of the cloud is negative
Polarized cloud induces the ground to be polarized
Lightning occurs to neutralize the charge imbalance

19. Electric Shielding
Why is it safe to drive stay inside a car during a lightning storm?
Excess charges only coat the surface of an object
Object’s normal electrons force the extra electrons to stay outside
Inside of the car remains neutral
Same with the inside of a Van de Graaff generator

20. Lab – Mapping Electric Potential
Groups of up to 3
You will measure the electric potential difference with a volt meter
Measure 36 (6 x 6) points around the positive terminal
Measure 6 points from the negative terminal to the positive terminal
Draw contour map at 0.5 V intervals
Turn in drawing