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 is a list that ranks objects’ ability to take negative charges

Electrostatic Series:

RubberEbonitePolyethyleneCottonSilkWoolGlassAcetateFur / Hair

Items at top take negatives

Items at bottom lose negatives

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

Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair

Rubber

Fur / Hair

Items at top take negatives

Negatives

Rubber balloon

becomes negative

Cat’s fur becomes positive

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

Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair

Wool

Polyethylene

Items at top take negatives

Negatives

Polyethylene balloon

becomes negative

Wool becomes positive

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

Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair

Cotton is +

Silk is -They would

ATTRACT

You then bring the charged piece of cotton & the charged piece of silk

together. What will happen?

+

-

-+

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.

• 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.