1. Charging Objects
Physics A
Static #2

2. Learning Targets
I can summarize the process of charging by friction, including the types of charges objects acquire and why.

3. Charging by Friction
The frictional charging process results in a transfer of electrons between the two objects that are rubbed together.
Rubber has a much greater attraction for electrons than animal fur.
As a result, the atoms of rubber pull electrons from the atoms of animal fur, leaving both objects with an imbalance of charge.
The rubber balloon has an excess of electrons and the animal fur has a shortage of electrons.
Having an excess of electrons, the rubber balloon is charged negatively.
Similarly, the shortage of electrons on the animal fur leaves it with a positive charge.
The two objects have become charged with opposite types of charges as a result of the transfer of electrons from the least electron-loving material to the most electron-loving material.

4. The Law of Conservation of Charge
Charge is not created from nothing.
Electrons are transferred in any charging process.
Prior to the charging, both objects are electrically neutral.
The net charge of the system is 0 units.
After the charging process, the more electron-loving object may acquire a charge of -12 units; the other object acquires a charge of +12 units. Overall, the system of two objects has a net charge of 0 units.
Law of Conservation of Charge: Charge is always conserved. When all objects involved are considered prior to and after a given process, we notice that the total amount of charge amidst the objects is the same before the process starts as it is after the process ends.

5. During a physics lab, a plastic strip was rubbed with cotton and became positively charged. The correct explanation for why the plastic strip becomes positively charged is that ...
a. the plastic strip acquired extra protons from the cotton. b. the plastic strip acquired extra protons during the charging process. c. protons were created as the result of the charging process. d. the plastic strip lost electrons to the cotton during the charging process.

6. Which statement best explains why a rubber rod becomes negatively charged when rubbed with fur?
a. The rubber that the rod is made of is a better insulator than fur. b. The fur is a better insulator than the rubber. c. Molecules in the rubber rod have a stronger attraction for electrons than the molecules in the fur. d. Molecules in the fur have a stronger attraction for electrons than the molecules in the rubber rod.

7. Saran Wrap has a larger electron affinity than Nylon
Saran Wrap has a larger electron affinity than Nylon. If Nylon is rubbed against Saran Wrap, which would end up with the excess negative charge? Explain.

8. Learning Targets
I can use text and diagrams to determine the resulting charge distribution when a charged object is brought near a neutral object.
I can explain the process of charging by induction.

9. Charging by Induction
Induction charging is a method used to charge an object without actually touching the object to any other charged object.
Charging WITHOUT TOUCHING

10. Charging a 2-Sphere System Using a Negatively Charged Object

11. Charging a 2-Sphere System Using a Positively Charged Object

12. Charging by Induction

13. The Importance of a Ground in Induction Charging
A ground is simply a large object that serves as an almost infinite source of electrons or sink for electrons.

14. Two neutral conducting pop cans are touching each other
Two neutral conducting pop cans are touching each other. A positively charged balloon is brought near one of the cans as shown below. The cans are separated while the balloon is nearby, as shown. After the balloon is removed the cans are brought back together. When touching again, can X is ____.
a. positively charged c. neutral
b. negatively charged d. impossible to tell

15. Two neutral conducting pop cans are touching each other
Two neutral conducting pop cans are touching each other. A positively charged glass rod is brought near Can X as shown below. Which of the following occur as the glass rod approaches Can X? List all that apply.
a. Electrons jump from the glass rod to can X.
b. Electrons jump from the glass rod to can Y.
c. Electrons jump from can X to the glass rod.
d. Electrons jump from can Y to the glass rod.
e. Protons jump from the glass rod to can X.
f. Protons jump from can X to the glass rod.
g. ... nonsense! None of these occur.

16. TRUE or FALSE?
Two neutral conducting pop cans are touching each other. A negatively charged balloon is brought near Can X as shown below. As the balloon approaches Can X, there is a movement of electrons between the balloon and can X (in one direction or the other).

17. A positively charged balloon is brought near a neutral conducting sphere as shown below. While the balloon is near, the sphere is touched (grounded). At this point, there is a movement of electrons. Electrons move ____ .
a. into the sphere from the ground (hand)
b. out of the sphere into the ground (hand)
c. into the sphere from the balloon
d. out of the sphere into the balloon
e. from the ground through the sphere to the balloon
f. from the balloon through the sphere to the ground
g nonsense! Electrons do not move at all.

18. Suppose that a negatively charged balloon is used to charge an electroscope by induction. The procedural steps are described in the educational cartoon below.
On the cartoon, draw the orientation of the needle and indicate the location and type of any excess charge in steps ii. - v. Explain in terms of electron movement what is happening in each step.

19. A negatively charged balloon is brought near a neutral conducting sphere as shown below. As it approaches, charge within the sphere will distribute itself in a very specific manner. Which one of the diagrams below properly depicts the distribution of charge in the sphere?

20. A positively charged piece of Styrofoam is placed on the table
A positively charged piece of Styrofoam is placed on the table. A neutral aluminum pie plate is brought near as shown below.
While held above the Styrofoam, the aluminum plate is touched (grounded). At this point, there is a movement of electrons. Electrons move ____ .
a. out of the aluminum plate into the ground (hand)
b. into the aluminum plate from the ground (hand)
c. into the aluminum plate from the Styrofoam
d. out of the aluminum plate into the Styrofoam
e. from the ground through the aluminum plate to the Styrofoam
f. from the Styrofoam through the aluminum plate to the ground
g nonsense! Electrons do not move at all.

21. Learning Targets
I can summarize the movement of subatomic particles that results after charged objects have been touched and then separated.
I can identify objects that could serve as effective grounds in electrical situations.
I can compare the process of charging by conduction using a positively charged object and using a negatively charged object.

22. Charging by Conduction
Charging by conduction involves the contact of a charged object to a neutral object.
Charging by TOUCHING

23. Charging by Conduction Using a Positively Charged Object

24. Charging by Lightening
Rather than being a process in which the two objects act together to share the excess charge, the process of charging by lightening could best be described as the successful effort of electrons to burst through the space (air) between objects.
The presence of a negatively charged insulator is capable of ionizing the air surrounding it and allowing excess electrons on it to be conducted through the air a neutral object.
This transfer of charge can happen with or without touching.

25. Charging by Lightening
In fact, on a dry winter day the process of charging a conductor with the charged insulator often occurs while the insulator is some distance away.
The dry air is more easily ionized and a greater quantity of electrons is capable of bursting through the space between the two objects.
On such occasions, a crackling sound is often heard and a flash of light is seen if the room is darkened.
This phenomenon, occurring from several centimeters away, certainly does not fit the description of contact charging.

26. A neutral metal sphere is touched by a negatively charged metal rod
A neutral metal sphere is touched by a negatively charged metal rod. As a result, the sphere will be ____ and the metal rod will be ____. Select the two answers in their respective order.
a. positively charged
b. negatively charged
c. neutral
d. much more massive
e. ... not enough information to tell

27. A neutral metal sphere is touched by a negatively charged metal rod
A neutral metal sphere is touched by a negatively charged metal rod. During the process, electrons are transferred from the _____ to the _____ and the sphere acquires a _____ charge.
a. neutral sphere, charged rod, negative
b. neutral sphere, charged rod, positive
c. charged rod, neutral sphere, negative
d. charged rod, neutral sphere, positive
e. ... nonsense! None of these describe what occurs.

28. A neutral metal sphere is touched by a positively charged metal rod
A neutral metal sphere is touched by a positively charged metal rod. During the process, protons are transferred from the _____ to the _____ and the sphere acquires a _____ charge.
a. charged rod, neutral sphere, negative
b. charged rod, neutral sphere, positive
c. neutral sphere, charged rod, negative
d. neutral sphere, charged rod, positive
e. ... nonsense! None of these describe what occurs.

29. A metal sphere is electrically neutral
A metal sphere is electrically neutral. It is touched by a positively charged metal rod. As a result, the metal sphere becomes charged positively. Which of the following occur during the process? List all that apply.
a. The metal sphere gains some protons.
b. Electrons are transferred from the sphere to the rod.
c. The metal sphere loses electrons.
d. The overall charge of the system is conserved.
e. Protons are transferred from the rod to the sphere.
f. Positive electrons are moved between the two objects.

30. Grounding - the Removal of Charge
Objects with an excess of charge - either positive or negative - can have this charge removed by a process known as grounding.
Grounding is the process of removing the excess charge on an object by means of the transfer of electrons between it and another object of substantial size.
When a charged object is grounded, the excess charge is balanced by the transfer of electrons between the charged object and a ground.
A ground is simply an object that serves as a seemingly infinite reservoir of electrons; the ground is capable of transferring electrons to or receiving electrons from a charged object in order to neutralize that object.

31. Grounding a Negatively Charged Object

32. Grounding a Positively Charged Object

33. The Need for a Conducting Pathway
Any object can be grounded provided that the charged atoms of that object have a conducting pathway between the atoms and the ground.

34. A positively charged pop can is touched by a person standing on the ground. The pop can subsequently becomes neutral. The pop can becomes neutral during this process because ______.
a. electrons pass from the pop can to the person (ground)
b. electrons pass from the person (ground) to the pop can
c. protons pass from the pop can to the person (ground)
d. protons pass from the person (ground) to the pop can

35. A physics student, standing on the ground, touches an uncharged plastic baseball bat to a negatively charged electroscope. This will cause ___.
a. the electroscope to be grounded as electrons flow out of the electroscope.
b. the electroscope to be grounded as electrons flow into the electroscope.
c. the electroscope to be grounded as protons flow out of the electroscope.
d. the electroscope to be grounded as protons flow into the electroscope.
e. the baseball bat to acquire an excess of protons.
f. absolutely nothing to happen since the plastic bat does not conduct.

36. TRUE or FALSE:
An object that becomes grounded gains neutrons during the grounding process.