Electricity Unit

Chapter 11: Static Electricity

11.1 What is Static Electricity?

Atomic Structure and Electric Charge

___________________ is a form of charge, either positive or

negative, that exerts an electric force.

Recall that an atom that has an electric charge is called an

_____. A
______________ ion is an atom that has picked up one or more electrons. A
_________________ ion is an atom that has lost one or more electrons.

Properties of the Particles of an Atom

Positive, Negative, and Neutral Objects

Everyday objects such as combs, rulers, clothing, airplanes, and clouds are made up of billions and billions of
atoms—each containing a number of positive and negative charges. For this reason, it is impossible to show
individual atoms or their charged particles in diagrams of large objects.

Charge Symbols
We use _________________________ to represent charges. Each charge symbol represents a very large
number of protons (+) or electrons (–).

● A “+” symbol will be used to represent a large number of __________________ (carrying positive
charges)
● A “–” symbol will be used to represent an equally large number of ________________ (carrying
negative charges)

These symbols will be used to show the relative ______________________________________ of charges

on an object. The overall electric charge of an object can be determined simply by
______________________________________________________________ drawn on the object.

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Matching:

(a)

(b)

(c)

Detecting Static Electric Charges

An _______________________ is an instrument that scientists can use to detect the

presence of electric charges.

A ___________________________________consists of a ball of pith (plant material)

suspended from a stand by a thread. It can be used to test for the presence and type of
electric charge on an object.

This is done by bringing an object near the neutral pith ball. If the object is charged, the
pith ball will be attracted to it.

A _______________________________________ is more sensitive to electric charge than a pith ball

electroscope and is more commonly used to detect electric charge.

When a negatively charged object is brought near the electroscope electrons are transferred into the leaves,
which causes them to repel and spread apart (b) until the charged object is removed (c).

The Law of Electric Charges

A charged object exerts an ________________, which can be either an ________________ force (pulling
together) or a __________________ force (pushing apart).

This is summarized in ___________________________, which states that

• objects that have like charges repel each other
• objects that have opposite charges attract each other

Electric Force
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The ______________ of the electric force is related to both the amount of charge on each object and the
distance between the charged objects.

Electric force is greater with increasing electrical charges and becomes weaker as the distance between
objects increases.

Like charges repel Opposite charges attract

Attraction of Neutral Objects to Charged Objects

When a charged object is brought near a neutral object, it causes (or ______________) the electrons to shift
in position. The induced movement of electrons in a neutral object by a nearby charged object is called an
________________________________________.

● If the charged object is positively charged, it will induce electrons

in the
neutral object to move ___________ it
● If the charged object is negatively charged, if will induce
electrons in the
neutral object to move ________ from it

Using Static Charges

Scientists and engineers can use the properties of static charges in many useful
ways in a branch of science called electrostatics. ______________ is the branch of science that deals with
static charges and static electricity.

Electrostatic Paint Sprayers

Electrostatic paint sprayers use the properties of
static
charges to more efficiently paint objects. The
paint is
given a charge as it leaves the nozzle of the
sprayer,
and the object to be painted is given the opposite
charge.

Homework: Read section 11.1 and complete

questions
2 - 9 on pg. 471
11.2 Charging by Contact
Charging Objects by Friction

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Charging by friction occurs when two different ____________ materials are rubbed together or come in
contact (touch) and electric charges are ______________ from one object to the other.

One material is more likely to _________ extra electrons and become ________________ charged, while the
other material is more likely to _______________ electrons and become ____________________ charged.

This is because some kinds of atoms are more strongly

attracted to electrons than others.

Example of Friction
During contact, or when being rubbed together, each
material is
charged. For example, in Figure (a), the hair and the comb
are
both ___________. When they are rubbed together, the
atoms in
the comb __________ electrons and the atoms in the hair
__________ electrons (Figure (b)).

The Electrostatic Series

The electrostatic series is a list of materials in order of increasing
___________________________________. As you move further
down the
list, the materials increase in their tendency to gain extra electrons.
We can
use the electrostatic series to predict the charge that will be gained by
two
objects or materials that are rubbed together.

Think, Pair, Share!

You rub a piece of wool against your skin. What charge does each
material
now have?

You grab a rubber balloon with a wool glove on your hand. What
charge
does each material now have?

Charging Objects by Conduction

Charging by conduction occurs when two objects with ____________
amounts of electric charge come in
contact and electrons move from one
object to the other.

This can occur between:

● A charged object and a neutral
object
● Two charged objects

A Neutral and a Charged Object →

Two Charged Objects

Two charged objects may come in contact, and
electrons may move from one object to the other. Electrons always move from the object with a ___________

negative charge (less positive) to the object with the __________ negative charge (more positive). This
produces a more even distribution of electric charge between the two objects.

The electric charge is not _________________ in the two pieces of metal after they come in contact, but they
both now have the same ________
and _____________ of charge.

If a positively charged piece of metal

comes
in contact with another identically
sized
piece of metal that has less positive
charge
(Figure 5(a)), electrons will travel
from the
less positively charged piece to the
more
positively charged piece until both
pieces
have an even distribution of charge (Figure
5(b)). After contact, the two pieces of metal
each still have a positive charge (Figure
5(c))

Grounding
Objects with an ______________ electric charge—either positive or negative—can have the excess charge
removed by a process called ____________. Grounding an object involves ___________________________
_____________ by transferring electrons between the object and a large neutral object such as Earth (the
ground). Any object that serves as a seemingly infinite reservoir of electrons can be used as a “ground” for
electric charges. For example, because Earth is so large, any excess charge is spread over a huge area and is
effectively neutralized.
● When a positively charged object is grounded, electrons from the ground travel up to the positively
charged object until the object is neutral.
● When a negatively charged object is grounded, electrons travel from the object into the ground until the
object is neutral.

What happens when you get a shock?

 (a) Before the discharge, the hand is negatively charged and the faucet is neutral. (b)
During the discharge, excess electrons are transferred from the hand into the ground.

(c) After the discharge, the negative charge on the hand has been
removed.

Putting Charged Objects to Work

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Advances in electrostatics have led to the development of many useful products and technologies. Several of
these involve charging objects by contact (friction or conduction).

______________________________ depend on charging by friction to attract dust.

An _______________________________ is a device that uses the properties of

electrostatic charge to remove particles from the air. Electrostatic precipitators are
used in large power plants, manufacturing plants, and incinerators.
 Homework: Read section 11.2 and
answer questions #1-6

11.4 Conductors and Insulators

Practical Implications
Conductors are materials that ___________ the movement of electrons.
Insulators are materials that _______________ the movement of electrons.
Both conductors and insulators have practical applications.

Conductors

_________ conductors allow electrons to move through them with ease. __________
or semi-conductors allow electrons to move through them with a small amount of
difficulty.

The most familiar conductors are ____________ such as copper and aluminum.
These metals can be used in the wiring that appears in electrical cords in appliances.

Think pair share!

Could you place a charge on a conductor if you were holding it in your hand?
_____________________________________________________________________

Real life applications

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Salt water is listed as a fair conductor since it contains ions, which pass through salt water easily. On the other
hand, pure water is considered non-conductive since it does not contain ions.

What about the water in your home? Why do warning labels tell us not to use electrical appliances near water?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
Insulators
Insulators are the answer to using electricity safely. In an insulator,
the electrons are tightly bound to the atoms that make up the
material, so they are __________________________ to
neighbouring atoms. _____________________, such as wood and
plastic, are good insulators.

Real life applications

Electrical wires in homes are coated with an
_______________________________, such as plastic. Insulators protect
us from the danger of having large amounts of electric charge move
through our bodies if we come in contact with a conductor. Placing a
plastic insulator around a copper wire prevents electrons from escaping
the conductor. In this way, the electrons stay in the conductor and discharges are avoided.

Using conductors and insulators

A _____________________ is a common household electrical device that requires the properties of both
insulators and conductors. A laser printer consists of a drum made of a _______________________________
________________________________ which only conducts electrons when a light (laser) is shined on it.

1. The laser light quickly “draws” the image to be printed across a ______________________________
__________________________, causing these areas to become negatively charged. 2. When the drum
is rolled over paper that has been given a __________________________________ than the drum, the
positive toner particles become attracted to the negative paper.
3. The paper then passes through a fuser that melts the toner particles, which are made from plastic, onto
the paper using temperatures of over 200 °C.

Homework: Read
11.4 and answer #1,
3, 6, 7

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11.6 Charging by
Induction

The process of charging a neutral object, either

temporarily or permanently, by bringing another
charged object , but not touching, the neutral
object.

Charging Objects Temporarily by Induction

When a charged object is brought near a neutral object it causes (___________) the electrons to shift in
position, resulting in an ___________________________________________.This will only be
___________________ as the electrons will move back to their original positions once the charged object is
taken away.
Real World
Example
When a computer monitor or television screen is turned on it begins to build up a charge.
When a neutral dust particle comes near the screen, the charge on the screen induces an
__________________________ on the__________________________
____________________ and a similar charge to that on the screen, on the far side. The
result is that the _______________________________________.

Charging Objects Permanently by Induction

Recall that is connecting an object to a large body, like Earth, that is capable of effectively
removing an electric charge that the object might have. An object can be charged by induction
by grounding the object.

An Example

(a) When a negatively charged ebonite rod is brought near a neutral pith ball, the electrons in the pith ball
are repelled and it becomes temporarily negatively charged on its right side.
(b) Attaching a ground wire to the pith ball conducts the repelled electrons on the right side into the ground.
(c) After removing the ground wire, the pith ball remains permanently positively charged.

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Think Pair Share!
After a charge has been induced on the neutral object, what do you think will happen if
you touch the neutral object on the side that has a negative charge?

An important thing to note!

Charging by induction always results in two objects with opposite charges.
● The object that induces the charge ________________________________________ ●
The object whose charge was induced ________________________________________

Useful Applications of Charging by Induction

An ___________________________________________ can be used to make a copy of
a footprint left behind at a crime scene. A special film or foil is placed over the footprint.
The black side of the film is placed over the footprint. The film is then electrostatically
charged. The dust and dirt particles from the footprint are attracted to the black side of
the film. The dust particles “jump” off the floor onto the black film, revealing the details of
the footprint.

________________________________ operate on the principles of induction. These speakers are

constructed of three thin layers. The outer two layers, called stators, are fixed in place and are made
of a porous material. The inner layer is a flexible film called the diaphragm. In order to produce
sound, the diaphragm must vibrate. This is accomplished using the principles of induction and the
Law of Electric Charges.

First, the inner surface is given a permanent

electrical charge. Then an audio transformer is used to
induce opposite charges in the two outer plates. This
causes the diaphragm to move—as it is simultaneously
attracted to one outer plate and repelled by the other
(Figure a).
The audio transformer then rapidly induces the static
charges in the outer plates to reverse themselves. This causes the diaphragm to now move toward the
opposite outer plate (Figure b).

This reversing of charges on the outer plates happens repeatedly and at variable frequencies causing the
diaphragm to rapidly vibrate back and forth between the plates, producing sound waves in the air.

Homework: Read section 11.6 in your textbook and answer questions #2, 3, 5, 6

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11.8 Electric Discharge

What Causes Electric Discharge?

When two objects that have a charge imbalance are brought close together or come in
contact, electrons are transferred from one object to the other object. We call this rapid
transfer of excess charge an _______________________.

Electrons leave one object and pass into another object. Electrons always move from the object with the
_________ negative charge (less positive) to the object with the _________ negative charge (more
positive). Discharges can sometimes be seen as ________________. The greater the
_______________________, the larger and more noticeable the discharge will be.

Lightning
Lightning is a very dramatic electric discharge. It happens as a result of a charge
imbalance____________________, or ______________________________________________.

The excess negative charge at the bottom of the cloud repels the electrons at Earth’s surface. Electrons move
away from the area on Earth’s surface near the cloud, causing it to become positively charged.

The overall result is a charge imbalance between the bottom of the cloud and Earth’s surface.

How it works
If the charge imbalance becomes great enough, the excess electrons may be rapidly transferred from the
cloud to the ground in the form of lightning. The resulting large transfer of electrons causes the surrounding air
to become _______________. This produces both the flash of light and the rumbling sound of thunder.
________________________________________________________________________________________
_____________________________________________________________________.

Lightning Rods
To minimize the danger of lightning to people and structures, lightning rods are
often placed on top of buildings to provide a
____________________________________________________________. A
lightning rod is usually made of metal, such as iron or copper. There is also a
wire
that goes from the rod into the ground.

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Chapter 12: Electrical Energy Production

12.1 & 12.2 Current Electricity and Electric Circuits

Current Electricity:

Current electricity moves _______________ through a conductor and

________________ through an insulator.

It can be very dangerous to touch a conducting wire that has electricity through it since human skin is
considered to be a fair conductor. Therefore, conducting wires are wrapped with ___________________
material (i.e. plastic) which ___________________ the flow of electricity from entering your body. Instead, it
gets held up in the insulator.

In order for electricity to flow it needs a _______________________ and a ____________________ to move

through. The power source gives the electrons ___________________________ and the conductor gives the
electrons ____________________________.

Circuits

An electric circuit is a __________________________ in which electrons can flow.

Fig. 1 A simple circuit

Electric circuits consist of 4 basic parts:

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1.

→ provides ______________ energy to the circuit.

Battery

2.

→ device that _____________ electrical energy into another usable form of energy i.e. light bulb
converts electrical energy into heat and light.

Bulb Motor

3.

→ device which ________________ the electric ______________.

(turns the circuit on or off)

Switch

4.

→ ________________ all of the components of the circuit and allow electricity to flow through the circuit. I.e.
Copper is an excellent conductor, is inexpensive and has low resistance.

Connecting wire

**Energy sources include batteries and generating stations

Homework: pg 508 #2 - 6 and pg 510 #2 - 6

Read section 12.3 and answer #3-7 on pg 514

12.4 Forms of Current Electricity

There are two forms of current electricity:
 1. __________________________________

2. __________________________________

Direct Current (DC)

● A flow of electrons in _______________ through an electric
circuit.
● Produced by an _______________ (battery).
● Powers portable electrical devices (ex. toys).

Alternating Current (AC)

● A flow of electrons that _____________ in direction in an
electric circuit.
● Produced by ______________ at generating stations.

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● Efficient method of distributing electricity over long
distances. ● Ex. wall outlets

Generating Electricity
● Generating stations convert mechanical energy into electrical energy.

1. External Energy source turns a TURBINE.

2. The turbine spins a COIL OF WIRE inside a magnet, producing electricity.

External
Energy:
Steam
Wind
Moving
water
Benefits:
● Can travel long distances.
● Flow of electrons is controlled.
● Can be converted into other types of energy.

Types of Energy
● Motion → washing machine
● Thermal → toaster
● Light → lamp

12.5 Generating Current Electricity

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Read section 12.5 in your textbook and complete the following table.
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Energy Nuclear Sun/Solar 15
Source How does it work?
Renewable or
Fossil Fuels Nonrenewable?
Advantages Disadvantages

Biomass
Water/
Uranium/ Hydro
Geothermal

Tidal

Wind

12.7 Electrical Power and Efficiency

Electrical Power – the rate at which electrical energy is _________________ or ______________.

Unit of measurement – __________________

The higher the wattage, the greater amount of energy a device produces (or uses to
operate). Which requires/uses more energy, a 40W or 60W light bulb? ________

Power = Energy or
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time
SYMBOL UNIT
Power P Watts (W)
Energy E Joules (J)
Time t Seconds (s)

Example
1. How much energy does a 1200 W dishwasher use when it runs for 20 minutes?

Measuring Electrical Energy Usage

Since the unit joule is relatively small, we often measure electrical energy in units of watt∙hours (W∙h),
kilowatt∙hours (kW∙h), or gigawatt∙hours (GW∙h).

Kilowatt∙hour is ___________ times greater than watt∙hours and gigawatt∙hours is _______________ times greater than
kilowatt∙hour.

The amount of electrical energy that is used in homes, schools and businesses is kept track by electricity meters in
units of kW∙h.

Percent Efficiency

If an electrical device were perfect, all of the electrical energy that it uses would be converted into the desired
form of energy. Most appliances are not 100% efficient.

Efficiency is _________________________________________
__________________________________________________
___________________________________________________.

○ Fluorescent light bulbs are ______________ more efficient than regular

incandescent bulbs
○ Other examples:
○ __________________________ –
use less energy than their
competitors (on televisions,
computers, etc.)
○ _________________ labelling
system on large
appliances (washer/dryers,
dishwasher) that gives
details about the amount of energy
that an
appliance uses in one year of
normal use to help
make informed choice when
buying appliances.

How much energy the appliance uses in

one year

How it compares with similar appliances

 on the market

We can calculate % Efficiency from the following formula:

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% Efficiency = Energy output (Eout) x 100%
Energy input (Ein)

Where Eout = Total amount of the desired form of energy produced

Ein = Total amount of energy required for the device to work

Examples

2. Determine the % efficiency of a 60 W fluorescent bulb that uses 2000 J of electrical energy to produce
1760 J of energy?

3. An electrical kettle has a power rating of 100 W. It takes 4 minutes to boil the water. If it takes 1.96 x
105 (196 000 J) of energy to boil the water, what is the efficiency of the kettle?

All homes are now installed with smart meters. The smart meter is an electrical energy meter that is
connected to your home and measures the ____________ of electrical energy being used as well as the
_________ at which it is being used.

Cost of Electricity

○ Our government charges different rates (according to the time of day) for electricity usage
○ It is important to understand how much is charged for energy consumption

Cost to operate = power used × time × cost of electricity

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Example
 4. A laptop computer uses a 75 W adapter when it is plugged in. Electricity costs 5.6 cents / kW•h.
Calculate how much it would cost to operate the laptop for 1 year for 24 hours/day.

Homework: Pg. 535 #2-7

Chapter 13: Electrical Quantities in Circuits

13.1 Circuit
Diagrams
Circuit diagrams are a pictorial way of
showing circuits. Electricians and
engineers draw circuit diagrams to help them
design the actual circuits. Here is an example
circuit diagram.

Circuit diagrams show the connections as

clearly as possible with all wires drawn neatly
as straight lines.

Table 1 Common Circuit symbols

Electric cell Two cell battery

Electrical conductor
Three cell battery

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Open switch Closed switch

Light bulb Motor

Series Circuits
● Loads are connected end to end so that there is only ________ path for the electrons to
flow.

Circuit Diagram
Parallel Circuits
● Loads are connected by branches so that there are _____________________ paths for electrons to
flow.

Circuit Diagram
Your electrical panel at home contains fuses which regulates a number of series circuits (i.e. lights in
the bedroom vs. lights in the kitchen) but all the series circuits are connected in parallel to each other.
Therefore, when the fuse that regulates the lights in your bedroom blows, the lights in your kitchen still
work.

Try this with a partner!

Using the circuit symbols you just learned, draw a circuit diagram for the following circuit.

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For the circuit above, does the lightbulb light up?

Practice:

a) Draw a circuit diagram showing an open switch, a two cell battery and three light bulbs and one
motor connected in series.
 b) Draw a circuit diagram showing a three cell battery and two light bulbs and a motor connected in
parallel. Include a switch for controlling each load. Show one switch to be open.

Measurements in Current Electricity

A cell or battery provides energy to push negative charges through the conductors in a circuit. This movement
of charge is known as current. More specifically, current (I) is the amount of charge (Q) moving past a point in
a conducting wire every second (t).

Current = charge moving past a point time Did you know???

1 coulomb is equal to:

I=Q
Current t
Charge
Time Symbol Unit (quantity)

6 250 000 000 000 000 000 electrons = 6.25 x 1018 e

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That’s A LOT of electrons!!!
To measure current in a circuit a device called an ______________ is used. In order to measure current,
connect the ________________ by breaking the circuit, and making the device as part of the circuit.

It’s circuit symbol is:

Ex. Kettle = 12.5 A

Toaster = 8.8 A
Radio = 0.4 A
Very small amounts of electric current are dangerous!
The maximum level of current considered to be safe is
0.005 A. Anything above this value causes muscles to
contract and to remain contracted until the source of
electrical current is removed. Breathing muscles can
become paralyzed, the heart can stop pumping, and the
person can become unconscious and die.
 Using the GUESS method to solve problems

Ex.1 If 340 C of charge passes through a conducting wire in 5.0 minutes, what is the current? Ex. 2

How much charge passes through a wire every 2.0 minutes, if the current has a value of 1.52 A?

Homework: Pg. 554 # 1-7

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Current & Charge Calculations Worksheet
Characteristics of Electricity – Measuring
Electricity

Q current = charge moving past a point 1. Find the unknown quantity:

time I = Q Units: I is A (amperes) t Q is C
IT (coulombs) t is s (seconds)
a) I = 0.4A Q = b) I = ? c) I = 2 A
t = 20 s Q = 240 C t = 300 s Q = 400 C t = ?

2. Find the unknown quantity (CONVERT FIRST to seconds)

a) I = PROBLEMS b) I = 0.3 A
Q = 140 C Q=
t = 4 min = _______ s WORD t = 1.5 hours = _______ s
c) I = 0.9 A
Q=
t = 3 min = _________ s
1. If there is a current of 10 amperes in a circuit for 10 minutes, what quantity of electric charge flows in
through the circuit?

2. How much current must there be in a circuit if 100 coulombs flow past a point in the circuit in 4 seconds?

3. How much time is required for 10 coulombs of charge to flow past a point if the rate of flow is 2 amperes?

13.3 Electric Current

Electric current is a measure of the _____________________________

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_________________ in a circuit. The symbol for current is I and the unit is
A (amperes).

An ammeter is a device that is used to measure electric current.

The circuit symbol for an ammeter is:
Safety
At home, if too much current is running through the circuit breaker or fuse,
it
__________ or ___________ and behaves like an open switch,
_______________ the flow of current. The helps to avoid electronics from
becoming damaged by electric currents.
Measuring current: An ammeter must be connected in series with a load to
measure the current flowing through the load
When using an ammeter:
● Always set the ammeter to the __________________ current setting. Too low a setting can damage
the meter.
● To prevent an electric shock, ____________________ the tips of the ammeter leads when they are
connected to a circuit.

The Human Body and Electrical Shock

Your body works by sending electrical signals through the nervous system. Instead of electrons travelling
through your body, charged particles called ___________, are sent through the nervous system (ie. Na+ and
K+).

Even small electrical shocks can be dangerous

● 0.001 A passing through the body may give you a _______________________
● 0.050–0.150 A can cause muscles to contract or convulse out of control; you can no longer
___________ of the object that is shocking you
 ● 1.0–4.3 A passing through the chest will _______________________
● A wall outlet that powers a computer can deliver 15 A

Homework: Read section 13.3 in your textbook and answer questions #1, 3, 4

13.5 Potential Difference

Potential Difference is __________________________________________
_________________________________ (i.e. negative and positive terminal of a battery). It is measured in
____________ (V).
You can imagine this as a little bit of water spilled on your table. The water will not flow until your table is
unleveled. If you tilt the table to any side, leading to a difference in level over the table, the water will start to
flow from the higher level to the lower one.
A ___________________ is used to measure potential difference.
The circuit symbol for voltage is:

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A voltmeter must be connected in ______________ with a load or an
energy source since it is measured between two locations. There is
always a drop in voltage across a load or energy source.

Example
Draw a circuit that contains: a closed switch, a 2 cell battery, 2 light bulbs in series, an ammeter measuring the
current between the two bulbs and a voltmeter measuring potential difference across one of the bulbs.

Potential Difference in Series Circuits vs. Parallel Circuits:

 Homework
:
Read section 13.5 and answer questions 2-4.
Potential Difference Calculations Worksheet
Characteristics of Electricity – Measuring Electricity

potential difference = energy is C (coulombs) E is J (joules)

charge

1. Find the unknown quantity: 25

V = E Units: V is V (volts) Q Q
a) V = ? b) V = 9 V E = ? c) V = 1.5 V E = 225 J
E = 45 J Q = 15 C Q = 150 C Q=?

2. Find the unknown quantity (CONVERT FIRST to volts, joules, or coulombs)

a) V = 1000 mV = ______ V E = ? WORD PROBLEMS 1500 C

Q = 20 C b) V = ? c) V = 1.21 GV =_________V E = ?
E = 1.25 kJ = _________ J Q = Q = 2 000 000 C

1. The potential difference between the two terminals on a battery is 9 volts. How much work (energy) is
required to transfer 10 coulombs of charge across the terminals?
2. Ten joules of work (energy) are required to transfer 2 coulombs of charge from X to Y. What is the
difference in potential between these two points?

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3. It requires 600 joules of energy to transfer a quantity of charge between points C and D of a circuit, which
have a potential difference of 30 volts. How much charge is transferred?

13.7 Resistance in Circuits

Resistance: refers to the ability of a conducting substance to _________ down the flow of
______________(electrons).

o All conductors and loads (lights, motors, etc.) have some resistance.
o Having resistance in an electrical circuit _____________ the amount of current.
o Resistance is the __________ you feel from the adapter when you recharge your cell phone or have
your laptop plugged in.
o An _______________ is a device to measure resistance and it must be placed in
______________________________.
o The circuit symbol for an ohmmeter is:
o The symbol for resistance is _______ and the unit is ________ (Ω).

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o A _________________ is a device that reduces the flow of electric current. (i.e. a dimmer switch is an
example of a resistor)
o The circuit symbol for a resistor is:
 All materials have some ____________________. The ______________ the resistance, the _________ the
current, and the _____________ the material becomes when current flows through it. As the electrons move
through the material, they bump into the atoms that make up the material. In the process,
__________________ is converted into ___________________. Internal resistance depends on many factors:
type of material, cross-sectional area, length, and temperature.

Knowing the resistance of materials is very important for electrical engineers. There are four factors that affect
the resistance of a wire.

1. Length: When the length of a wire increases, the electrons have _______ wire to travel through.
Therefore, the resistance ___________ when length ____________. If the length doubles, the
resistance _______________.
2. Cross Sectional Area: When the cross sectional area of a wire increases, the electrons have
_________ space to move around and therefore the resistance __________________. If the cross
sectional area doubles, the resistance is ___________.

higher resistance lower resistance

Smaller cross sectional area higher cross sectional
area

3. Temperature: Different materials can heat up fast when

current is moving
through it. As the temperature of the wire increases, the resistance ___________________. 4.
Material: Some materials allow electrons to move more freely than others and therefore have a
____________ resistance.Conductors, such as copper, have low electrical resistance.
Consider the following: You’ve changed the wires of a circuit so they have a smaller cross sectional area
(the wire is thinner). What happened to the resistance?

Homework: Read section 13.7 and answer questions 2-4, 6, & 7.

Resistance Calculations Worksheet

Characteristics of Electricity – Measuring Electricity

V resistance = potential difference R = V Units: R is Ω (ohms) I V is V

current (volts)
RI
1. Find the unknown quantity: b) I = ? c) I = 15 A
R = 200 Ω V = 240 V R=?
a) I = 10 A I is A (amperes) V = 110 V
R = 1500 Ω
V=? 28
2. Find the unknown quantity (CONVERT FIRST to the unit with no prefix)

a) I = ? PROBLEMS b) I = 25 mA = _________ A R = ?
R = 2000 Ω V = 110 V
V = 20 mV = ________ V WORD c) I = 1 kA = ________ A R = ?
V = 50 mV = ________ V
 1. How much resistance does a light bulb create if it has a current of 25 mA around it in a 9 V circuit?

2. A heating coil offers a resistance of 2.5 kΩ. What voltage is required so that 1.5 A of current pass through
it?

3. The human body offers a very small amount of resistance (let’s say 1 mΩ for argument). If a lightning bolt -
said to have 1.21 GV of potential according to a famous movie called Back to the Future released in 1984- hits
you, how much current is flowing through your body?

13.9 Relating Current, Voltage, and Resistance

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The relationship between the amount of resistance in a circuit and the voltage and current in a circuit is called
________________________.

Consider a wire with a certain resistance:

R=V If voltage____________, current ___________. If voltage

I ____________, current ___________.

Resistance: symbol R, units ohm’s (Ω)

Voltage: symbol V, units volts (V)

Current: symbol I, unit amperes (A)

Example

A cordless curling iron with a resistance of 18 ohms allows 0.5 amperes to flow through it. How much voltage
is provided by the curling iron? Use the GRASS method.

Measuring Resistance
 You can determine the resistance of a simple resistor by studying the relationship between
____________________ and _______________. You would set the potential difference (V) at several
different values and observe the current (I). You would then plot current (I) vs. potential difference (V) and
calculate the slope. The ___________ of the line is equal to the ___________________ (R).

Calculating Slope

Table of Current and Voltage Readings for a Series Circuit

Current (A) Voltage (V)

0.0 0.0

0.03 0.6

0.05 1.0

0.10 2.0

30
0.20 4.0

0.40 8.0

*In order for the load (resistor) to be ohmic, the line must be straight!

a) From the table above, calculate the resistance of the circuit in the space provided. b) Graph the data on the following
page. Ensure that you include a title, and label your axes.
 31

Homework: Read section 13.9 and answer questions #2 -9.

Graphing Resistance Assignment

13.10 How Series and Parallel Circuits Differ

Resistance in Series Circuits

● Less resistance results in ____________ current

● More resistance results in ___________ current

If you compare two series circuits, the first having only 1 bulb while the second
having 2 bulbs, the second series circuit will have _________ current flowing
through each of the 2 bulbs than the first circuit since there is more
__________________. Electrons flowing through the second circuits have more
_____________ along the way.

Example

1. The same type of lightbulb is used in two series circuits. The first circuit has
two identical light bulbs. The second circuit has three identical light bulbs.
The potential difference across the battery is 10 V. The circuit on the left as
a total resistance of 10 Ω . The circuit on the right has a total resistance of
15 Ω. Use the total resistance given to calculate the current through each circuit.
 32

Voltage in Series Circuits

In a series circuit, the potential difference of the battery (source) is split over the total number of loads.
Therefore, if the potential difference of a battery is 6V and there are two bulbs, each bulb would receive 3V of
potential energy to convert into light and heat.

We can express this mathematically with the following formula:

Vload = Vsource
# of loads

Example

2. A series circuit contains four identical bulbs. The voltage across the energy source is 96V. Calculate
the voltage across each lamp.

Current in Parallel Circuits

Since electrons have different paths to take in parallel circuits, current will be split in however many paths
there are. The number of paths depends on the number of loads connected in parallel.

We can express this mathematically with the following formula:

33
Iload = Isource
# of loads

Example

3. A parallel circuit contains four identical bulbs. The potential difference across the energy source is 48V.
The total resistance of the bulbs is 12 Ω. Calculate the current through each bulb.
Resistance and Voltage in Parallel Circuits

● When loads are connected in parallel, the total resistance will be less than if the loads were connected
in series.
● The voltage measured across each parallel load will be the same as the total voltage provided by the
source.

Example

4. A parallel circuit contains 10 identical bulbs. The current through the energy source is 3.0 A. The total
resistance of the circuit is 15 Ω. Calculate the voltage across the energy source and across each bulb.

Summary of Relationships of Loads in Series and Parallel Circuits:

34

Mixed Electricity Problems

Characteristics of Electricity – Measuring Electricity

**DON’T FORGET TO CHANGE TO THE UNIT WITH NO PREFIX FIRST!

**ALL OF THESE NEED TWO DIFFERENT FORMULAS

1. How many coulombs of charge pass through a 95 W amplifier plugged into a 110V wall socket over the
course of a 2 hour concert.
 2. A bulb plugged into a 110V wall socket has a resistance of 100 Ω. Find how many seconds it takes to pass
2000 C of charge.

35
3. 2500 coulombs of charge is passed over a 2 hour period across a certain capacitor. What is the resistance
of this capacitor if the voltage across it is 200 mV.

4. What is the power of a microchip that passes 1 C of charge with a potential difference of 0.01 mV in 1
second.

36
37
5. A simple circuit has a 9V battery attached to it. How long does it take to pass 1C of charge through that battery if its
resistance is 150 Ω.
6. What is the current in an electric stove element that creates 150 J of heat at 240 V over a 5 minute period. 38