Exercise 2: Basic Electricity Concepts
Objective
At the end of this exercise students should be able to define in their own words concepts of
electricity, voltage, current and electrical loads.
Introduction
In order to understand how electricity works we must first understand what electricity is.
The basic atom model, described by Niels Bohr in 1913, presents electrons
as relatively free particles, with negative charge, moving in layers around a
positively charged nucleus. Electrons in layers farthest away from the
nucleus experience a weaker attraction to the positively charged nucleus
and can be forced to move from one atom the next if the right conditions
exist. Such conditions can come about by changes in factors like
temperature, the proper combination of chemicals and materials, or rubbing
two bodies against each other, leading to the formation of an electromotive
force field.
Electromotive force fields, also known as voltages and measured in Volts (V), come about from the
difference in potential energy between the materials or two points in the same material. Under the
influence of a voltage, the constant random motion of electrons becomes organized into a flow of
electrons. This organized flow of electrons is commonly refer to as an electric current and is
measured in Amperes (A). As electromotive force fields become stronger, more electrons will be
forced to move. Thus, for the same material, larger currents result from larger voltages.
Static electricity is a form of electricity in which electrons transfer from one material to the next and
become locally stored. The excess or loss of electrons causes the body to become temporarily
charged and allows it to attract other bodies with opposite charge. The body releases the stored
charge when a path to a body with lower electric potential exists. The lowest possible electric
potential is called ground. A path to ground on a body charged with static electricity causes an
immediate discharge.
Static electricity is detrimental to many electronic components such as computers as the sudden
discharge of static electricity can burn transistors inside integrated circuits. It is for this reason that
such industries requires the installation of special conducting tiles and have in place strict
electrostatic discharge (ESD) policies.
Knowledge gathered through years of experimentation lead us to modern day technology. Today,
we have two main categories of electric systems: direct current (DC) and alternating current (AC).
The two forms consist on a flow of electrons through the material. The difference among them has
to do with the behavior of those electrons through time. For DC systems, electrons move in the
same direction at a constant rate. For AC systems, electrons move back and forth and their
velocity profile follows a sinusoidal wave.
Current
Current
Time
The magnitude of the
current in a DC system
is constant.
Time
The magnitude of the
current in an AC system
follows a sinusoidal wave.
AC electricity is somewhat more complex and will be dealt with in a later exercise. For now, let’s
focus on DC systems. Voltage sources for DC systems include batteries, solar cells,
thermocouples, DC generators and hydrogen cells. Batteries are, by far, the most common type of
DC voltage sources used.
(The following information is taken from http://science.howstuffworks.com. The site has plenty of
additional and interesting information on the subject. Students are urged to visit the site and get the
full story.)
Battery Basics
If you look at any battery, you'll notice that it has two terminals. One terminal is marked (+), or
positive, while the other is marked (-), or negative. In an AA, C or D cell (normal flashlight
batteries), the ends of the battery are the terminals. In a large car battery, there are two heavy lead
posts that act as the terminals.
Electrons collect on the negative terminal of the
battery. If you connect a wire between the
negative and positive terminals, the electrons will
flow from the negative to the positive terminal as
fast as they can (and wear out the battery very
quickly -- this also tends to be dangerous,
especially with large batteries, so it is not
something you want to be doing). Normally, you
connect some type of load to the battery using
the wire. The load might be something like a light
bulb, a motor or an electronic circuit like a radio.
Inside the battery itself, a chemical reaction
produces the electrons. The speed of electron
production by this chemical reaction (the battery's internal resistance) controls how many electrons
can flow between the terminals. Electrons flow from the battery into a wire, and must travel from
the negative to the positive terminal for the chemical reaction to take place. That is why a battery
can sit on a shelf for a year and still have plenty of power -- unless electrons are flowing from the
negative to the positive terminal, the chemical reaction does not take place. Once you connect a
wire, the reaction starts.
The first battery was created by Alessandro Volta in 1800. To create his
battery, he made a stack by alternating layers of zinc, blotting paper
soaked in salt water, and silver, like this:
This arrangement was known as a voltaic pile. The top and bottom layers
of the pile must be different metals, as shown. If you attach a wire to the
top and bottom of the pile, you can measure a voltage and a current from
the pile. The pile can be stacked as high as you like, and each layer will
increase the voltage by a fixed amount.
The excerpt above talks about batteries, but also about connecting their terminals to loads using
wires. That is called a circuit. When the components are connected so that there is a continuous
path for the current to flow between the terminals of the battery, the circuit is known as a closed
circuit. An open circuit, on the other hand, would be a circuit in which such a continuous path does
not exist. No current flows through open circuits.
The term load refers to the device we connect to the circuit. Examples of loads are light bulbs,
motors, buzzers, computers, stereos, cell phones, electronic toys, etc.
Magnetism
Molecules in ordinary metals are polarized. This means that each molecule has a positive and a
negative side. Yet, these molecules are randomly arranged so that the overall material is not
polarized. The presence of a magnetic field around a metal, however, will cause these molecules
to rotate and align with the magnetic field. The end result is a magnet.
When an electric current flows through a conductor, it induces a magnetic field around the
conductor. It is possible to concentrate the magnetic field by forming a coil with the wire. If such
coil is wound around a metal, the metal will become temporarily magnetized. That is known as an
electromagnet.
Demo 1: Static Electricity (Demo performed by the Instructor)
Materials

4” * 2” piece of foam

1 Sheet of tissue paper
Procedure
1) Place some small pieces of tissue paper on the table.
2) Rub the foam piece on your hair for a few seconds.
3) Hold the foam close to the tissue pieces.
Test 1: Building a battery
Materials

Multimeter set-up to measure voltage

30 Zinc washers

30 Aluminum washers

30 nickels

30 pennies

Small pan or shallow dish

5 sheets of tissue paper

Salt

Vinegar
Try this!!
Insert a Zinc nail and a
Copper nail into a lime so they
are close by, but not touching
inside or outside. Touch it
with your tongue for the tingly
sensation of a current flow.
Procedure
1) Pour vinegar into the shallow pan and add salt. Mix until the salt dissolves.
2) Cut rings of tissue paper the size of washers or nickels
3) Separate the washer and coins in three groups each.
4) Follow the process outlined below for each pair on tokens. Start with Zinc washers & pennies,
continue with Zinc Washers & nickels, Zinc washers & Aluminum washers, nickels &
Aluminum washers, pennies & Aluminum washers, and nickels & aluminum washers.
1. Soak a tissue ring in the vinegar and place it on the Zinc washer.
2. Top the tissue with a penny so as to make a tissue sandwich with the tokens.
3. Stack ten of these sandwiches so that pennies are always followed by Zinc washers.
5) Measure the voltage across each stack and record your readings in the table below
Battery Components
Zinc & Aluminum
Zinc & Nickel
Zinc & Penny
Aluminum & Nickel
Positive Terminal of Multimeter
connected to
Voltage Reading
Battery Components
Positive Terminal of Multimeter
connected to
Voltage Reading
Aluminum & Penny
Nickel & Penny
Test 2: Magnetism
Materials

One “D” battery

Iron bolt (3” or 4”)

Thin copper wire (bare, about 2 meters long)

Paper clips of same size
Procedure
1) Tightly wrap the cooper wire around the bolt to form a coil leaving about 4” of loose wire on
each end.
2) Hold the ends of the coil one on each side of the batteries.
3) Bring the bolt next to the paper clips and count the number of clips you are able to pick.
Battery Components
Zinc & Aluminum
Zinc & Nickel
Zinc & Penny
Aluminum & Nickel
Aluminum & Penny
Nickel & Penny
Demo 2: Circuits
Materials

One “D” battery

Rubber band
Number of Clips Picked up

Light bulb holder and light bulb

Small motor

Buzzer

2 pieces of Cooper wire (insulated, about 8” to 10” long)

Multimeter set-up to measure current
Procedure
1) Remove the insulation from the each end of each cooper wire (about ½ in).
2) Place the rubber band around the long side of the battery so it passes over the poles.
3) Slide one end of a wire under the rubber band so it is in contact with the positive pole of the
battery. Do the same with the other conductor and the negative pole of the battery.
4) One at a time, connect the lamp, the motor and buzzer
5) Measure the current flowing through the circuit with each load.
Load
Current Measured
Lamp
Motor
Buzzer
Review Questions
1) Explain in your own words what electricity is.
2) Explain in your own words what voltage is.
3) Explain in your own words what current is.
4) Explain in your own words what electrical loads are.
5) What are the units to measure voltage and current?
6) What is a closed circuit?
7) What is the difference between AC and DC systems?
8) How do batteries work?
9) What is magnetism?