Lesson 2 ­ Charging by Contact
April 25, 2014
11.2 ­ Charging by Contact
Several ways to charge objects with static electricity:
1) Charging by Friction
• Rubbing two different objects together
2) Charging by Conduction
• Two objects with different charges coming in contact
3) Charging by Induction
• A charged object is brought close to a neutral object
Friction – rubbing two different substances together eg. rubbing a balloon in your hair
> to determine what charge an object will have depends on the substance it is made from
> An Electrostatic Series is used to tell the charge on substance: if the substance is closer to the top, it will have a weaker hold of its electrons and will become positively charged
Lesson 2 ­ Charging by Contact
April 25, 2014
Electrostatic Series
Charge tendency
Material
+ (weaker tendency to gain electrons)
(stronger tendency to gain electrons)
­­
Human Skin
Rabbit fur
Acetate
Glass
Human hair
Nylon
Wool
Cat fur
Silk
Aluminum
Paper
Cotton
Wood
Amber
Rubber
Vinyl
Polyester
Ebonite
Polyethylene/plastic
Copper
Gold
TRY: state the charge on each object
1) cat rubs up against your cotton jeans
2) gold ring rubbing against wool mittens
3) rubber assembly belt carrying plastic wrapped package
4) cotton and wool socks in a dryer
5) for a comb in the winter which is best plastic or aluminum
Lesson 2 ­ Charging by Contact
April 25, 2014
Conduction: two different amounts of electric charge come into contact.
• electrons move from one object to another
• two objects get SAME overall charge
• can cause sparks and shocks
Grounding
•
•
•
•
removing excess charge
transferred to a large neutral object such as the Earth (ground)
postive objects receive electrons
negative objects lose electrons
the symbol for grounding
Lesson 2 ­ Charging by Contact
Usefulness of static electricity
Electrostatic paint sprayers
Electrostatic dusters
Electrostatic precipitators
April 25, 2014