Electric force

Do Now

1. Electric force2. Towards the attracting object3. Charge was transferred from the cloth to the

ruler. Pieces of paper were attracted to the ruler by the electric force. Gravity acts against the electric force and tries to keep the paper on the table.

Do Now

4. Object demonstrates electric interaction after rubbing

5. Objects rub together (this is only one way!)

6. Same charge repel

7. Different charge attract

Do Now

8. Material through which a charge will not easily move

9. Material that allows charges to easily move

10. Electrons can move easily

11. Air is an insulator because charges do not easily move

DEMO

Electroscope

Electroscope

• Electroscope=metal knob connected by metal stem to two thin, lightweight pieces of foil called leaves

Metal Knob

Thin metal stem

Lightweight foil leaves Container

Observation 1: Initial Conditions

• What are the initial conditions for the electroscope?

• Where are the charges located and how many of each type are there?

Observation 2: Separation of charge

• As the charged rod is brought closer, what happens to the leaves?

• What happens to the charges?

Observation 3: Conduction

•What does the charged rod do?•What is the effect on the leaves?•What happens to the electrons on the rod?•What do the leaves do after the rod moves away?

Observation 4: Induction

•What does the charged rod do?•What is the effect on the leaves?•What happens to the electrons on the rod?•What do the leaves do after the rod moves away?

EXPLANATIONSWhat just happened?

Observation 1: Initial Conditions

• Foil leaves close together• neutral charge – same amount of +

and - charges

Observation 2: Separation of charge • As the charged rod is brought

closer, leaves move apart

Polarize – separate into opposites

Polarize: + and – charges separate within the object

Check for Understanding & Summary

• What were the initial conditions of the electroscope?

• Define polarization.• How did the electroscope become polarized?– Negatively charged rod brought close to metal ball– + charges concentrate on metal knob, - charges

concentrate in the leaves

Observation 3: Conduction

•Conduction: transferring electrons by touching a charged object to another object

Observation 3: Conduction1. Charged object touches

the other object

Rod touches the top of the electroscope

Observation 3: Conduction2. Electrons transferred between the objects• Electrons flow from rod to

electroscope• This is b/c they repel each other

and want to be far from each other

Observation 3: Conduction3. Remove charged object. Other object is now charged• Remove rod• Electroscope has neg.

charge• Leaves move away from

each other

Check for Understanding & Summary

• Define conduction• Explain each step of conduction

Observation 4: Induction

Induction – transferring electrons by holding a charged object next to another object

Observation 4: Induction

1. Charged object polarizes other object• Rod polarizes

electroscope• + charges concentrate on

metal knob, - charges concentrate in the leaves

• Leaves spread apart

• Objects do not touch• e- DO NOT leave the

rod!!!

Observation 4: Induction2. Second object is grounded and electrons are transferred

– Person touches electroscope

– e- flow from electroscope, into person, into ground

e- DO NOT leave the rod!!!

Observation 4: Induction

3. Remove ground and remove charger– Person removes hand

and removes rod

4. Object is now charged

– Electroscope has + charge– Leaves move away from each other

Check for Understanding & Summary

• Define induction• Explain each step of induction

Key Point

• Law of Conservation of Charge – overall charge on a system is the same before and after the charging process

Charges do not disappear, only transferred from one source to another

ELABORATELet’s expand upon what we just learned!

van de Graaff generator

Apply what you know!

• Independently answer the questions in your notes

Check for Understanding & Summary

• 1. Upper collecting comb becomes polarized: e- move to the bottom of the brush b/c they are attracted to the + rubber belt

• The upper comb is already grounded, so it becomes neg. charged by induction

Check for Understanding & Summary

• 2. Comb is attached to dome. Charge transferred from comb to dome by conduction

• 3. Person gets close to dome and gets shocked: negative charge transferred by induction

• 4. Person touches the dome – negative charge transferred by conduction

BACKUP

Observation 5: Induction part A

Observation 6: Induction part B

Observation 7: Induction Part C

Observation 8: Induction Part D