Science 9
Unit: Characteristics of Electricity
Chapter 8 – Voltage, Current, Resistance
& Ohm’s Law
Your Name: _____________________
Block: ______
8.1 Electric Potential Energy & Voltage
In order for electricity to be useful it must useful it must be stored and controlled. One of
the most common techniques to store electricity is a battery. A battery is a collection of
smaller units called electrochemical cells, which convert chemical energy to electric energy.
In these cells the positive and negative charges are separated resulting in terminals where
connections are made. When the terminals are connected, electrons at the negative
terminal travel to the positive terminal (opposite charges attract).
Where can batteries be found?
 Watches

 Laptops

Cell Phones
Vehicles (car & hybrid)


Cameras
Pace Makers
Every battery has two terminals called electrodes. Each electrode is usually made up of a
different metal that are sounded by substance called an electrolyte, which conducts
electricity between the two electrodes (positive is called the Cathode, negative is called the
Anode).
Different types of batteries:
 Alkaline
 Lithium Ion
 Silver Oxide
 Nickel Cadmium
 Nickel Metal Hydride
Exercise
Label the
following
parts of a Dry
and Wet cell
batteries.
Mr. Ostoforov
Common Electrodes:
 Zinc
 Nickel
 Copper
 Magnesium
 Lithium
Dry Cell
Revised Jan 25, 2011
Common Electrolytes:
 Acids
 Bases
 Salts
 Ammonium Chloride
 Potassium Hydroxide
Wet Cell
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Science 9
Unit: Characteristics of Electricity
Recall, energy is the ability to do work. There are types of energy: Kinetic Energy is energy
in motion and Potential Energy is stored energy. Since a battery stores energy until needed
it is said to have electric potential energy. The amount of electric potential energy per one
coulomb is called the potential difference or voltage (V). The unit for measuring potential
difference is the volt (V) named after the Italian physicist Alessandro Volta who invented
the first battery, the voltaic pile.
Since we cannot see charges and the
potential difference we use a device
called a voltmeter to measure the
voltage. To use a voltmeter you connect
one end of the device to one side of the
battery (red to positive) and the other
end to the other side of the battery (black
negative). If the voltage you get is
negative that means you have your
connections backwards.
Symbol:
Questions
Explain how a battery produces a potential difference between two electrodes.
How much voltage can modern electrochemical cells produce? How is a car battery able to
produce 12 V?
Mr. Ostoforov
Revised Jan 25, 2011
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Science 9
Unit: Characteristics of Electricity
8.2 Electric Current
In order to utilize electric potential energy in a battery a connection has to be made from
one electrode to another electrode, this connection is called an electric circuit. Generally,
within an electric circuit we want to transform electrical energy into another form of energy,
which is called the electric load of the circuit.
What are some examples of an electric load?
 Light Bulb Light

 Speaker  Sound

Heater  Heat
Car Starter  Mechanical
There are many different kinds of circuits that perform a variety of operations; however,
there are four (4) basic kinds of components in a circuit, which include:
Explanation
Source
Were the electrical energy
comes from (e.g. battery)
Conductor
How the electric energy
travels from the source
(e.g. wire)
Load
A device that transform
electric energy into
another form of energy
(e.g. light bulb)
Switch
A device that can turn the
circuit on or off by opening
or closing the circuit
Symbol
There are many ways one can explain an electric circuit, but the most common and easiest
way is with a circuit diagram. A circuit diagram uses symbols to represent the different
components of the circuit. In order for a circuit diagram to be useful it must be organized
correctly as well as:




Neat and tidy (i.e. use a ruler)
Make all connecting wires and leads with straight-lines at 90o angles (i.e.
perpendicular).
Avoid drawing conductors over top one another (use a semi-circle if unavoidable)
Your finished diagram should be square or rectangular.
Mr. Ostoforov
Revised Jan 25, 2011
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Science 9
Unit: Characteristics of Electricity
Without a complete circuit the battery has nowhere to push electrons. With a competed
circuit, electrons flow from the negative terminal through a conductor, to a load, then
finally to the positive terminal of the battery. This flow of electrons within a circuit is called
current (I) and can thought of as concept of electricity.
Electric current is defined as the amount
of charge passing a point in a conductor
every second. It is measured in ampres
(A), named after the French physicist
André-Marie Ampére. In order to
measure current we use a device called an
ammeter. Unlike a voltmeter where you
connect across two points in a circuit, an
ammeter must be connecting inline with
the circuit. (note: 1.0 A = 1000 mA).
Symbol:
According to Benjamin Franklin he believed charged objects flowed from positive to
negative as the positive charge contained more ‘electric fluid’. This is contrary to our
current understanding were electricity flows form negative to positive. For historical
reasons we refer to Franklin’s idea as conventional current as it is still used today to
calculate potential difference in a circuit.
8.3 Resistance & Ohm’s Law
As electrons flow through a circuit, they do not do so unobstructed. As we saw with
insulators and conductors some objects transfer electrons more effectively that others. In
circuits we use the term resistance (R) to measure how easily electrons flow in a circuit. For
example the filament (tungsten) in a light bulb resist the movement of electron and in the
process creates a large amount of heat that makes the filament glow to create light.
A simple Hydraulic Analogy to Explain Circuits
The water flowing through the pipes is like the electrons flowing in a circuit. Voltage can be
thought of as a pump, pushing water through the system (i.e. more pressure); the larger
the pump (battery) the more water (electrons) goes through the system. The sizes of the
pipes restrict the flow of water in the system: the larger the pipe (lower resistance) easier
for the water to flow, smaller the pipe (higher resistance) harder for the water to flow.
In 1827, Georg Ohm a German physicist found a relationship between voltage, current and
resistance. Now referred to Ohm’s Law states that the electrical resistance of a circuit is
directly proportional to voltage and inversely proportional to current (or the ratio of
voltage to current). The unit for resistance is the Ohm ().
Mr. Ostoforov
Revised Jan 25, 2011
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Science 9
Unit: Characteristics of Electricity
𝑅=
𝑉
𝐼
𝑜𝑟
𝑉 = 𝐼𝑅
Exercises
Convert the following mA and A. 1 mA = 1/1000 A:
a) 12.0 mA = __________ A
b) 0.075 A = ___________ mA
Convert the following k Ω and Ω. 1 k Ω = 1000 Ω
a) 3.0 k Ω = ____________ Ω
b) 45, 000 Ω = ___________ k Ω
Convert the following MV and V. 1 MV = 1, 000, 000 V
a) 14 MV = ____________ V
b) 6,000,000 V = ________ MV
What is the resistance of a flashlight bulb if there is a current of 0.75 A through the bulb
when connected to a 3.0 V battery?
𝑅=
𝑉
3.0 𝑉
=
= 4.0 Ω
𝐼 0.75 𝐴
What is the voltage across a 12k Ω load that allows a current of 6.0 mA?
𝑉 = (0.0060 𝐴)(12000 Ω) = 72 𝑉
When designing circuits it is important have a precise amount of
current or voltage at a particular point in order for some
electrical components to work properly. In order to regulate the
voltage and current at a particular point in a circuit a resistor is
used. A resistor is an electrical component that has a specific
resistance. Resistance can be measured with a special device
called an ohmmeter.
Symbol
Resistors serve a very important function in circuits and as a result there are many different
sizes. Since resistors are so small, colour bands are used to identify its size. Each colour
corresponds to a particular number and it position on a resistor is the placeholder of that
digit.
Mr. Ostoforov
Revised Jan 25, 2011
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Science 9
Unit: Characteristics of Electricity
To read a resistor correctly the first band
represents the first digit, the second band
represents the second digit, and the third
band is the power of ten (10) multiplier (i.e.
the number of zeros that follow the second
digit). There is also a fourth band on a
resistor that represents how accurate the
resistor is to its indicated value.
Resistor Accuracy:
Mr. Ostoforov
Gold = 5%
Revised Jan 25, 2011
Resistor Colour Coding
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Silver = 10%
Numerical Value
0
1
2
3
4
5
6
7
8
9
No Band = 20%
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