Transcript Electricity PowerPoint

Electric Charges and
Currents
Atoms and Electricity
 All
matter is made up of atoms
 Parts of the atom
– positively charged (+)
 Neutrons – neutral (no charge)
 Electrons – negatively charged (-)
 Protons
 Where
 Move
are the electrons in an atom?
freely in the electron cloud
 Can be added and removed (form ions)
Atomic Model

“Cloud Model”
Atoms and Electricity
 Attraction
between particles that have
opposite charges
 Repulsion between particles that
have the same charge
 Like charges repel each other,
opposite charges attract (think about
magnets!)
Conductivity
 Some
materials allow electrons to
move through them easily –
Conductors – metals
 Some materials do not –
Insulators – plastic, rubber, wood,
glass
Electricity

Objects can develop electric charges
when their atoms gain or lose electrons
 Friction – rubbing two objects together
Van der Graaf generator
Electricity
– electrons flow from
one object to another through
direct contact
Electrical wires – copper
 Conduction
Investigate Charge Induction
Go to my website
 Click on Physical Science Websites
 Click on Unit 7 – Balloons and Static
Electricity
 Click Run
 Uncheck the Ignore Initial Balloon Charge
box
 Rub the balloon on the sweater and see
what happens when you stick it to the wall

Electricity
 Induction
– rearrangement of
charges
Balloon and paper
Static Electricity
 Static
electricity is the buildup of
electric charges on an object
 Once the charges build up, they do
not move
 The loss of static electricity is called
electric discharge
 Lightning
 “Shocking”
them
someone when you touch
Lightning
Investigate Static Electricity

John Travoltage
 Investigate the effects of different
variables on static electricity
Ohm’s Law
Gives us the relationship between voltage,
current, and resistance:
Voltage = Current x Resistance
V = IR

V
Set up the triangle!
I
R
Power
 Power
is calculated:
Power = Voltage x Current
 P = VI

 The
unit of power is watts
(W)
P
 Set up the triangle!
V
I
Current
Charges (electrons) can flow through a
conductor
 An electric current is a flow of charge
Current (I) is the amount of charge that
passes a given point per unit time
 Current is measured in amperes or
amps, (A)

Current

In order to have a current, there must be a
potential difference and a circuit
 Potential difference – the difference in
potential between two places –
measured in volts (V)
 Circuit – a closed path through which
electrons can flow
Current

Remember - thermal energy flows from
objects with higher temperatures to
objects with lower temperatures
 This is similar with electricity, except
instead of temperatures we have
charges
Greater Potential Energy  Lesser
Potential Energy
Flow of Electricity

When using electricity you want a
continuous flow of electrons through
whatever you are trying to power.
 If you have a potential difference
(usually from a wall outlet or battery), all
you need is a closed path or circuit
through which electrons can flow
 The flow of electrons through the circuit
is called the current
Flow of Electricity

In order to make the charges move and
keep moving, you need a device that uses
energy to do the work required to move
electrical charges
 Batteries
 Generators
Batteries
 Batteries
produce electricity by
converting chemical energy into
electrical energy
Resistance
The amount of current that can flow through
a circuit depends on
 Voltage
 How the wire resists the flow of electricity
 The opposition to the flow of electric charge
is called resistance (R)
 Resistance is measured in ohms (Ω)
 Anything that uses current creates
resistance

Circuits
Red
Blue
Yellow
Green
Series Circuits
 All
of the parts of a series circuit are
connected one after the other
 Only one path for the electrons
 If there is a break in the circuit, no
current
can flow
Parallel Circuits
 The
different parts of a parallel circuit
are on separate branches
 Several paths for the electrons
 If there is a break in one branch of the
circuit, electrons can still move
through other branches