1. Electrostatics and the Electric Field

2. 1. When the balloon is rubbed on the sweater, what might happen?

3. 1. When the balloon is rubbed on the sweater, what might happen?
A. Some positive charges in the sweater will move onto the balloon B. Some negative charges in the sweater will move onto the balloon
B Only the electrons can transfer. The positive charges are protons which cannot move.

4. 2. What do you think will happen when the balloon is moved closer to the wall?
Neutral wall
Negatively charged balloon

5. Some positive charges in the wall will move towards the balloon
2. What do you think will happen when the balloon is moved closer to the wall?
Some positive charges in the wall will move towards the balloon
Some negative charges in the wall will move towards the balloon
Some positive charges in the wall will go onto the balloon
Some negative charges on the balloon will go to the wall
A induction causes the electrons to move away. The positive charges are protons which cannot move.

6. 3. What do you think the balloons will do?
Negatively charged balloon
Negatively charged balloon

7. 3. What do you think the balloons will do?
The balloons will move towards each other
B. The balloons will move away from each other
C. The balloons will not move.
B. The negative charged bodies will repel one another.

8. 4. What might happen to the charge on the man when he touches the door knob?

9. 4. What might happen to the charge on the man when he touches the door knob?
Most electrons will go into the knob and down to the earth.
B. Some electrons will go from the earth through the knob and into the man.
A. Some electrons will go into the earth

10. Electric Force Charges create a force
The force causes objects to either repel or attract
Electric force is a non-contact force it causes action between charges without the charges coming in contact
Non-contact forces are often called “field” forces (like the gravitational force)
Start the generator and show the pie tins, wands, etc. Discuss what the generator is doing. Have one student volunteer to stand on the milk crate, touch the generator, and hold the rice krispies.

11. Electric Field
We can call the space around a charged object the electric field
The electric field exerts a force on objects within the field
The size of the force is based on the amount of charge present and the distance between objects

12. Electric Field The electric field is a vector quantity
It has a magnitude and a direction
The direction of the field can be measured using a positive test charge (as a standard)
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Show the pHet sim here and have students place charges in the field to see the lines when different combinations of charges are present.

13. Electric Field Lines
To show direction, electric field lines are drawn around the charges within an electric field
The electric field is stronger where the field lines are closer together
Arrows move away from a positive charge (because a positive charge repels the positive test charge)

14. Electric Field Lines
Electric field lines point toward a negative charge (because a negative charge attracts the positive test charge)
Electric field lines are also called lines of force

15. Electric Field Direction

16. Electric Field Magnitude

17. Note: If you substitute “F” from the Coulomb’s law equation into the “F” of the electric field equation, you get the following:

18. Example 1
There is an electric field in the atmosphere surrounding the Earth which has a magnitude of roughly 150 N/C and a direction pointing towards the center of the Earth. Determine the magnitude and the direction of the force experienced by a dust particle having a negative charge of 9.2x10-16 C.

19. Potential Energy
Review Potential energy is due to an objects position
All energy is measured
in joules
For an object to gain gravitational potential energy, work must be done on the object
Start Van de graff generator
Example: a book is lifted into the air and gains gravitational potential energy

20. Electric Potential Energy
The energy gained by an electric charge when work is done on the charge is called electric potential energy
Work is done on the charge when it is moved against an electric field
Example: A negatively charged balloon is pushed toward a Van de Graff generator
Once the charge is released, the electric potential energy becomes kinetic energy
Show demo of bubbles and balloon Have one student blow the bubbles and another student charge the balloon and move it towards the generator. Remind students that while the generator is creating an electric field, there are very few charges present.

21. Electric Potential
Electric potential is a comparison of the electric potential energy and the number of charges present
A balloon charged by rubbing it on your hair does not have many charges (only about 1 millionth of a Coulomb)
This is why a balloon doesn’t shock you . . .it can have high voltage, but not enough charge to harm you

22. Electric Potential

23. Example 2
How much energy is stored when 7.2 C of charge is moved through a potential difference of 1.5 V?

24. Review What is the space surrounding a charged particle called?
How does a charged particle gain electric potential energy?
Is the strength of an electric field effected by distance? If so, how?
What is a volt?
Electric field
Work must be done on the charge.
The field strength increases as the distance decreases.
1 Joule/1 Coulomb (unit for electrical potential)

25. Tesla Coil A high voltage transmitter
Allows us to enjoy television, automobiles, and just about every other electronic device
Wireless electrical transmission
X-rays, radio, wireless telegraphy all attributed to Nikola Tesla
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26. Lightning
LIGHTNING

29. Lightning Lightning can travel up to 140,000 mph
Produce temperatures of 54,000°F
Can form fulgurites (sand into glass)
Transfers 15 C of electric charge

30. What is lightning? A natural capacitor
Charges are polarized within a cloud
The top of the cloud becomes positively charged
The bottom of the cloud becomes negatively charged
The electric field induces a movement of electrons from the cloud down toward Earth

31. Lightning Strikes
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Make a lightning strike
environment/natural-disasters/lightning- interactive/

32. A lightning strike
The electric field causes ionization of the air surrounding the cloud
This results in a conductive substance called plasma
The lightning bolt begins as a step leader or flow of electrons from the cloud toward the ground
A positive streamer rises up from the ground
When the step leader and the streamer meet, a conductive pathway allows the excess electrons to move to the earth

33. Lightning Rod
A lightning rod is a protective measure for tall buildings, farm houses, etc.
Used to direct lightning strikes to the ground
This allows the excess electrons to flow into the ground and not into the house or building

35. True or False You are safe in a vehicle during a lightning storm.

36. Capacitance
Electrical energy can be stored in a device called a capacitor
Capacitors are found in nearly all electronic devices
Televisions, camera flash, computer
A capacitor must be charged
A capacitor is discharged when a conducting path is provided between the plates

37. Capacitors A device that stores charge
Made of 2 conductors separated by an insulator

38. The charge stored will SHOCK you if you are in the conducting pathway!!
Found in many electrical circuits- computers, televisions, camera flashes