Download Chapter 1 Introduction to Electricity

Chapter 1 Introduction to Electricity
Section 1 Electric Charge and Static Electricity
Notes
Electric Charge
•
•
All matter composed of very small particles  atoms
Atoms made of even smaller particles:
o Proton – charged
o Electron – charged
o Neutron – not charged
Charges Exert Forces
o Charge is a physical property.
o Objects can have:
 Positive charge
 Negative charge
 Neutral charge
o Charged objects exert a force – a push or a pull
o Law of electric charges states that like charges repel, or push away and opposite
charges attract – just like magnets!
The Force Between Protons and Electrons
o Protons  positive charge
o Electrons  negative charge
o Neutrons  neutral charge
 Protons and neutrons attracted to each other!
The Electric Force and the Electric Field
o The force between charged objects  electric force
o Electric force depends on two things:



Amount of charge on each object
 Greater the charge – the greater the electric force
Distance between the charges
 the closer the charges are – the greater the electric force is
Charged objects affected by electric force because of an electric field around
them.
 Electric field – the space around a charged object in which another
charged object experiences an electric force.
 Objects in this field can be attracted or repelled depending on their own
charge.
Charge It!
o
o
o
o
All atoms have equal numbers of protons and electron resulting in  No Charge!
Objects become positively charged when  lose an electron
Objects become negatively charged when  gain an electron
Objects can also become charged through:
 Friction – when electron are “wiped” from one object onto another.
 Conduction – when electrons move from one object to another by direct contact.

Induction – when charges in an uncharged metal object are rearranged without
direct contact with a charged object.
o Conservation of Charge
 When you change the charge of something by any means  no charges are created
or destroyed
 Amount of electrons and protons stay the same – they simply move.
 Because of the move it is said that the charge is conserved
o Detecting Charge
 Electroscope – used to see if something is charged
 Constructed from: glass flask, metal rod, rubber stopper, and metal leaves
 When the electroscope is not charged  the leaves hang straight
 When the electroscope is charged  the leaves spread apart or repel
Moving Charge
o Most materials are either conductors or insulators based on how material move through
them
o Conductor

Electrical conductor – a material in which charges can move easily
 Examples: metals such as  copper, aluminum, and mercury
o Insulators

Electrical insulators – a material in which charges cannot move easily because
electrons cannot move freely
 Examples: plastic, rubber, glass, wood, and air
Static Electricity
o Static electricity – the electric charge at rest on an object
 When something is static it not moving or changing – the charges of static
electricity do not leave the object – they stay charged.
 Example: Clothes in the dryer
 Clothes charged from friction
 Negative charges from some clothing transfer to other clothing
 Dryer stops – the transfer of charges stop
 Clothing an insulator so the clothing retains the electric charge build up –
RESULT  static cling!
Electric Discharge
o When static electricity eventually leaves is called – electric discharge
o Electric discharge – loss of static electricity as charges move off an object
o This process can happen slow or fast
 Quickly:
 Flash of light
 Shock
 Crackling noise
 Lightening
Lightning Dangers
o Strikes at the highest point in a charged area because it is the shortest path
o How lightning forms:
 Negative charges build up in a cloud because of water and air in the cloud
 Different parts of the cloud have different charges
 top of the cloud positive charges
 bottom of cloud negative charges
 The negative charges at the bottom of the cloud react with the positive charges
on Earth’s surface
 Most lightning happens within and between clouds
Lightning Rods
o Mounted so they are the tallest point on a building
 A pointed rod connected to the ground by a wire by connecting it to the ground
through a wire it is grounded
 Any object that is grounded provides a path for the electrical charge to move to
Earth
 Earth can absorb the electrical charges without causing damage
o They prevent the buildings from being damaged by lightning