Electricity

1. Electricity
• Charge – a physical property that can be
positive or negative
• Law of electric charge – like charges
repel, opposite charges attract
• Force between charged objects if an
electric field exist is called electric force
• 2 things affect electric force:
– Amount of charge
– Distance between the charges

2. • Electric field is the region around a charged
object
• An object becomes positively charged when it
loses electrons and negatively charged when it
gains electrons
• Objects become charged by friction,
conduction, induction
• Friction – when electrons are “wiped” from one
object to another (rubbing your hair with a
ballon)
•

3. • Conduction – electrons move from one
object to another by contact
• Induction – charges in a uncharged metal
object are rearranged without direct
contact to a charged object
• Electrical conductor – material which
allows charges to move freely
• Electrical insulator – material in which
charges can’t move freely

4. 3 ways to charge an object
Induction – no contact
Friction – rubbing
Conduction – must touch

5. • Static electricity – electric charge at rest
on an object (static – not moving)
• Electric discharge - the loss of static
electricity as the charge moves off the
object
• Electric discharges can happen quickly
with a flash of light, a shock, or a crackling
noise (lightening)

6. • Electric current - the rate at which charges
pass a given point (units amperes, A)
• AC – (alternating current) the charges
continually shift direction (plug outlets)
• DC – (direct current) the charges always move
in the same direction (battery)
• Voltage - difference between two points in a
circuit (units volts, V)
• Voltage is a measure of how much work is
needed to move a charge between two points,
the higher the voltage, the more energy released
per charge (9V, 12V, 120V, 220V)

7. • Resistance - the opposition to the flow of
charges (units ohms,Ω (R))
• The higher the resistance, the lower the
current
• Resistance depends on the material,
length, thickness and temperature
• Superconductor – super cooled material
that lowers resistance (magnets)

8. • Machines can change one form of energy
to another (conversion)
• Thermocouples change thermal energy
into electric energy and photocells change
light energy to electric energy
• Electric circuits are complete closed paths
that allows electric charges to flow

9. • Three parts to a circuit are:
• 1. Energy source (provides electric
charge)
• 2. Wires (allows charge to flow from point
to point)
• 3. Load (changes electric energy into
other forms of energy)
• EX: radio – electrical to sound

10. Batteries (power source)
Dry Cell Wet Cell

11. • Two types of circuits: series and parallel
• Series: all parts are connects in a single
loop in a one way path
• All current must pass through the
complete series for circuit to work
• Any interruption causes the circuit to fail
(Xmas lights)
• Useful in burglar alarms

12. Series Ciruit

13. • Parallel: loads are connected side by side
and current can travel on more than one
path
• When circuit is interrupted, circuit
continues to function regardless
• Homes are wired on parallel circuits and
can have different loads in the circuit

14. Parallel Circuit

15. • Circuit failures are usually caused by over
loads or damage to the structure of the
circuit
• Fuses and circuit breaks “fail over” and
automatically break the circuit to protect
circuit and property

16. • Electromagnets – temporary magnets that lose
their magnetism when electric current is
removed
• Electricity can produce magnet fields and can
cause metals such as iron and steel to act like
magnets
• Generator is a device that converts mechanical
energy into electrical energy by using magnets
and a coil of wire that creates magnetic fields

17. • Electric motors convert electrical energy
into mechanical energy that is used to do
work
• EX: motors in house hold appliances like
blenders and washing machines