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 series is 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

Ex #1 Items at top take negatives Rubber balloon becomes negative 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

Polyethylene balloon becomes negative 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

In a lab, you rub a piece of cotton & ebonite together In a lab, you rub a piece of cotton & ebonite together. Then you rub a piece of silk & wool together. Ex #3 You then bring the charged piece of cotton & the charged piece of silk together. What will happen? Rubber Ebonite Polyethylene Cotton Silk Wool Glass Acetate Fur / Hair - Cotton is + Silk is - + - They would ATTRACT +

Ex #4 1st Hair & balloon are both neutral 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.