1. Charging objects by contact

2. Learning goals
I will be able to explain how to charge objects by contact
I will be able to conduct an investigation into the transfer of electric charges by friction, conduction, and induction and produce labelled diagrams to explain the results

3. Recall… Law of electric charges
Law of Attraction
An object that is charged will attract an object that is oppositely charged or neutral
Law of Repulsion
Two objects that have the same type of charge will repel each other

4. Methods of charging Charging Objects by Induction
Temporary – Induced Charged Separation
Permanently
Charging Objects by Contact
Friction
Conduction

5. Example: Balloon Rubbing against your hair

6. Here’s my silly demo. The balloon will rub against the head and then pull away with the “hair” standing on end. You might need to explain what it’s supposed to be.
The next few slides show what is happening to the charges. These should run automatically.

7. - + - + + - - + - - + + + - + - - + - +

8. - - + - + + - - + - - + + + - + - + - +

9. - - + - + + - - + - + + + - + - + - +

10. - - + - + + - - + - + + + - + - + +

11. - - + - + + - - + - + + + + - + +

12. - - + - + + - - + - + +
Re iterate that the head an balloon each started off with the same number of positive and negative charges but the rubbing moved charges onto the balloon and off the head.
The balloon is now negatively charged and the head positively charged so that because opposites attract the hairs are attracted to the balloon
And because like charges repel the airs are pushed apart from each other. + + - + +

13. Charging objects by contact: friction
Occurs when two different neutral materials are rubbed together or come in contact (touch), they produce a net static charge
Since the two objects are made of different materials, their atoms will hold onto their electrons with different strengths
As they pass over each other, the electrons with weaker bonds are “ripped” off and transferred onto the other material

14. Example: Balloon Rubbing against your hair
The rubber balloon has a stronger attraction to electrons than the hair, and therefore pulls the electrons away resulting in a negative charge while the hair becomes positively charged.

15. How do we know which material will lose the electrons and which one will gain them?
ELECTRON AFFINITY
The tendency of a material to gain and hold onto electrons
Simply put, it refers to the amount of love that a material has for electrons.

16. Electrostatic series
A list of materials arranged by their likelihood to attract electrons
Used to predict resulting charges from contact
The lower the material is on the series, the weaker its hold on electrons

17. Electrostatic series Relative Charge Negative (-) Positive (+)
Material
Rubber
Ebonite
Polyethylene (plastic)
Cotton
Silk
Wool
Glass
Acetate
Cat’s fur
Charge Tendency
HIGH Attraction for Electrons
LOW attraction for electrons

18. You Try!
Relative Charge
Negative (-)
Positive (+)
Material
Rubber
Ebonite
Polyethylene (plastic)
Cotton
Silk
Wool
Glass
Acetate
Cat’s fur
Charge Tendency
HIGH Attraction for Electrons
LOW attraction for electrons
Your rub a piece of cat fur against plastic. What charge does each material have now?
Plastic is higher on the list than cat fur, therefore it has a greater attraction for electrons than cat fur.
Plastic will gain electrons from the cat fur and become negatively charged. The cat fur will lose electrons to the ebonite and become positively charged.

20. Charging objects by Contact: conduction
Occurs when two objects with different amounts of electric charge come in contact (touch) and electrons move from one object to the other.
This can happen between:
Neutral Object & Charged Object
Two Charged Objects

21. Conduction: Neutral Object & Charged Object
Between a neutral object and a charged object, the neutral object takes the charge of the charged object upon contact.
As a result of the contact, some of the excess electrons on the bar which are repelling each other, move onto the sphere.

22. negative
positive
Negatively Charged
Neutral Object becomes
Positively Charged
Neutral Object becomes
negative
positive
When a negatively charged object touches a neutral object, the object becomes negatively charged
When a positively charged object touches a neutral object, the object becomes positively charged

23. Conduction: Two charged Objects
Electrons always move from the object with a larger negative charge (less positive) to the object with the smaller negative charge (more positive).
This produces a more even distribution of electric charge between the two objects
Metal Rod X:
Metal Rod Y:
Overall Charge: +3
Overall Charge: +1

24. Conduction: Two charged Objects
Electrons always move from the object with a larger negative charge (less positive) to the object with the smaller negative charge (more positive).
This produces a more even distribution of electric charge between the two objects
Metal Rod X:
Metal Rod Y:
Overall Charge: +2
Overall Charge: +2

25. You Try!
If the following two objects are charged by conduction, what are their final charges?
(A)
(B)
Overall Charge: +1
Overall Charge: -1
Overall Charge:
Overall Charge:
Overall Charge: -5
Overall Charge: -3
Overall Charge:
Overall Charge:

26. You Try!
If the following two objects are charged by conduction, what are their final charges?
(A)
(B)
Overall Charge: +1
Overall Charge: -1
Overall Charge:
Overall Charge:
Overall Charge: -5
Overall Charge: -3
Overall Charge: -4
Overall Charge: -4

27. Insulators vs. conductors
These results depend on the type of material used:
Conductors: electrons move freely from atom to atom in this material
Examples: Metal, tap water
Insulators: electrons do not move freely between atoms in this material
Examples: wood, wool, rubber, wax
Semi-conductor (“Fair Conductor”): electrons can move fairly well in these non-metal materials
Examples: Human body, graphite, silicon
Silicon Transistors

28. Investigation: Charge it!
Follow all lab safety protocols
Groups of 4
One person from each group will gather all materials needed
Investigation is divided into:
Part A: Charging by Friction
Part B: Charging by Conduction
Part C: Charging by Induction
Read the procedure of each section thoroughly before commencing. Record your Observations.
Once all procedures have been completed, continue with the Discussion and Conclusion questions.
Due Wednesday May 27