Friction, Conduction and Induction

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# Friction, Conduction and Induction - PowerPoint PPT Presentation

Friction, Conduction and Induction. How do you charge an object?. There are three ways to charge an object: 1. Charge by Friction 2. Charge by Conduction 3. Charge by Induction. How do you measure “charge”.

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### Friction, Conduction and Induction

How do you charge an object?
• There are three ways to charge an object:

1. Charge by Friction

2. Charge by Conduction

3. Charge by Induction

How do you measure “charge”
• The unit of measure for electrical charge is the Coulomb (C). In equations it is symbolized by a “q”
• Eg: q = 900C
• One Coulomb is equal to the charge of 6.25 X 1018 electrons (-) or protons (+).
• That is to say, one Coulomb has 6.25 X 1018 electrons.
Charging Objects
• Most objects start out electrically neutral, but by CHARGING an object you create an imbalance in the number of electrons and protons; the object is then charged and is either positive or negative.
• You can charge an object through:
• Friction – the transfer of electrons from one object to the other
• Conduction – by having two objects TOUCH each other and transfer electrons from one object to the next.
• Induction – By inducing electrons to move from one object to the other.
Charging by Friction
• When two neutral objects are rubbed against each other, one object may pull electrons away from the other creating one positive object and one negative object.
Electrostatic Series:
• All objects begin neutral & can become positively or negatively charged
• A positively charged object has more positives than negatives
• A negatively charged object has more negatives than positives
Electrostatic Series:
• Electrostatic seriesis a list that ranks objects’ ability to take negative charges

Rubber

Items at top

take negatives

Ebonite

Polyethylene

Cotton

Silk

Wool

Items at bottom

lose negatives

Glass

Acetate

Fur / Hair

Items at top

take negatives

Ex #1

Your cat rubs against a rubber balloon. What will be the charge on the balloon? Your cat’s fur?

Rubber balloon becomes negative

Rubber

Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair

Cat’s fur becomes positive

Fur / Hair

Negatives

Items at top

take negatives

Ex #2

In a lab, you take a piece of neutral wool & neutral polyethylene & rub them together. What will be their charges?

Polyethylene balloon becomes negative

Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair

Polyethylene

Negatives

Wool

Wool becomes positive

Ex #3

In a lab, you rub a piece of cotton & ebonite together. Then you rub a piece of silk & wool together.

You then bring the charged piece of cotton& the charged piece ofsilktogether. What will happen?

Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair

-

Cotton is + Silk is -

+

-

They wouldATTRACT

+

Ex #4

You rub your hair with a balloon. Explain using words & pictures, why your hair “sticks up”.

1st Hair & balloon are both neutral

_

+

_

_

+

+

2nd Rubber balloon takes negative charges from the hair. So, balloon becomes negatively charged & hair becomes positively charged

+

_

+

_

3rd Since hair is positive & like charges repel, hair sticks up!!!

Charging by Conduction
• An object can be charged by touching it with another object that already has a charge. The resulting object will then have the same charge but weaker in strength than the original object.
Charging by Conduction
• This image shows how a positive charged object alters the charge on the globe via conduction.
Charging by Conduction
• This image shows how a negative charged object alters the charge on the globe via conduction
Charging by Induction
• Objects do not touch (one is charged, one is neutral)
• Proximity of the charged object causes (induces) the charges in the neutral object to separate.
Charging by Induction
• This image shows how a negative charged object alters the charge on the globe via induction.
Charging by Induction
• This image shows how a positive charged object alters the charge on the globe via induction.

Key Points to Remember

• Two types of charges – positive(+) & negative (-)
• “Opposites Attract”
• “Like Repel”
• Items at the top of the electrostatic series list take negative charges
• Only negative charges move
• Three methods to charge an object: friction, conduction, induction. These three methods are what cause static electricity.