Unit 34 Electricity

Unit 34
Concepts of Electricity
 What is electricity?

Electric Charge
 Do you remember how ions form in chemistry?

• Ions form when atoms gain or lose electrons. To
acquire their charge, positive ions lose electrons and
negative ions gain electrons.
• If electrons are lost to another atom, then an atom
would become positively charged.

• If electrons are gained from another atom, then an
atom would become negatively charged.

Electricity is a form of energy carried by the movement of electrons.

The electrons of some atoms, like those of copper and other metals, are
only loosely attached, which allows electricity to travel through these
materials easily. These types of materials are known as “conductors.”

An outside force—such as light, heat, pressure, or a chemical
reaction—can cause electrons to break free and get “bumped” from one
atom to the next. A sequence of electrons then passes from atom to atom.

This continuous flow of electrons from atom to atom through a conductor is
called electric current.

Electric Current =

Electric Charge
 Charges that are the same repel each other. Charges
that are different attract each other.

Electric Force
 An electric field is a region around a charged object
where the object’s electric force is exerted on other
charged objects.

Transferring Charge
 There are three methods by which charges can be
transferred to build up static electricity: charging by
friction, by conduction, and by induction.

What is Induction?
 When a substance gains a charge without touching
another substance, it is said to have gained its charge
through induction.
 Example: you are about to touch a door knob and you
get shocked!!!!!

Quick Quiz

 What happens when you get shocked by static
electricity?
 A. Electrons are transferred from one object to
another.
 B. Protons are transferred from one object to
another.
 C. Neutrons are transferred from one object to
another.
 D. Positrons are transferred from one object to
another.

Types of Current
 There are two types of current: direct current (DC) and
alternating current (AC).

• Batteries provide DC voltage to an object. There are several
types of batteries such as AAA, AA, C, D, 9 Volt. Of these
batteries, the 9 Volt provides the most voltage and the D
has the greatest amount of stored energy in it.

• Alternating current (AC) is a type of electric current you
find in your home. Alternating current is a flow of electric
current that will regularly reverse its direction. The electric
current can flow forwards and backwards!

Flow of Electric Charges
 Electric current is the continuous flow of electric
charges through a material.

An Electric Circuit
 An electric circuit is a complete, unbroken path
through which electric charges can flow.

Resistance
 Two factors that affect the resistance of water flowing
in a pipe are diameter and length. The diameter and
length of a wire also affect resistance in a circuit.

Ohm’s Law
 Increasing voltage increases the current

 Increasing the resistance will decrease the
current (if voltage is held constant).

• The relationship between voltage and current is
a directly proportional. This means that as one
variable increases, the other increases (or as
one decreases, the other decreases).

• The relationship between current and
resistance is inversely proportional. This means
as one variable increases, the other decreases Georg Ohms
and vice versa.

Electrical Equations
Voltage = Volts Current = Amps Resistance = Ohms

Volts = joules/coulomb
Amperes = coulombs/second

Voltage = Current x Resistance

Current = Voltage ÷ Resistance

Resistance = Voltage ÷ Current

Electrical Power = Watts
Question Answer
What is electric power? Electric power is the rate at
which electrical energy is
transformed into another form
of energy.

James Watt

Watts = Joules/second

Volts * Amps = Watts

Electric Power
 The rate at which energy is transformed from one form
to another is known as power. Power is measured in
watts (W).

Electric Circuits
• There are two main types of electrical circuits: series and parallel.

• In a series circuit the current must be distributed throughout the
elements of the circuit. This means that none of the elements are
getting the same amount of current as they would if they were
alone in the circuit.

• A parallel circuit allows more than one path for the current to
flow. This allows for multiple elements to be placed within the
circuit, and each of these elements will receive the same amount
of electricity, as it would if were the only element in the circuit.

Kilowatt Hours
 A Watt is a joule/second
 A kilowatt is 1000 watts
 So, if you multiply Watts * Time = Joules or total energy
consumed.

 For example if you have a 100 watt light bulb and leave it on
for 24 hours, it will be 100 joules/sec * 86,400 seconds =
8,640,000 joules or 8640 kilojoules.

 In terms of kilowatt hours it is 0.1 kw * 24 hours = 2.4 kwh

 They are the same measurement.

Features of a Circuit
 Simple symbols are used to diagram a circuit.

Series Circuits
 In a series circuit, there is only one path for the current to take.

 In this kind of circuit, if you have one Christmas light go out, then
they will all go out.

Parallel Circuits
 In a parallel circuit, there are several paths for the
current to take. So, if one segment is broken, the
others take on the extra current.

The multiple wires on this
Christmas light keeps it a parallel
circuit so one light burning out
does not take out the whole set.

Comparing and Contrasting
 As you read, compare and contrast series circuits and
parallel circuits in a Venn diagram like the one below.
Write the similarities in the space where the circles
overlap and the differences on the left and right sides.
Series Circuit Parallel Circuit

Only one Unbroken Several paths
path for path that for current to
current to has a take
take current

Electrical Equipment and Fires
 If electrical equipment is not
properly used and
maintained, it can cause fires.
The circle graph shows the
percentage of fires caused by
different types of electrical
equipment.

Grounding
 One way to protect people from electric shock and
other electrical danger is to provide an alternate path
for electric current.

Fuses and Circuit Breakers
 In order to prevent circuits from overheating, devices
called fuses and circuit breakers are added to circuits.

A fuse will break if the
current is too high, cutting
off the electricity

Blown Fuse
 When the current is too high (like after a lightning strike),
the fuse breaks and the circuit is no longer connected

Circuit Breaker

 With a breaker box, when the current gets too high, it
switches the switch off, breaking the connection and
protecting the electronic devices hooked up to it.

Unit 34 Electricity

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Unit 34 Electricity