Unit 3: Electricity – Part A
Important Concepts and Key Terms Guideline
Concept
Description/Notes
Static Charge
Electricity is an integral
part of our lives
Students complete a paired brainstorming activity looking at how they
use electricity in their daily lives
Static Electricity
The buildup of charge on an object; Static means “to stay”. So charges
stay with the object
Current Electricity
The flow of electric charge; no longer staying in one place
Neutral
No charge. The positive and negative charges are equal
Positive Charge
There are more positive charges (protons) than negative charges
(electrons)
Negative Charge
There are more negative charges (electrons) than positive charges
(protons)
How are objects charged?
All solid materials are charged by the transfer of electrons. Negative
electrons are smaller and float around the nucleus and are free to be
transferred to other objects if they are close or in contact with one
another!
How do charges on objects
change?

Electric Discharge
If an electron is removed from a neutral atom, a negative charge
has been taken away and the object is positively charged!
 If an electron is added to a neutral atom, a negative charge has
been added, making the object negatively charged!
 When the number of protons = number of electrons, the object is
neutral!
 Positively charged atoms need to gain electrons to become neutral.
Negatively charged electrons need to lose electrons to become
neutral!
The removal of electric charge from an object.
Ex: Lightning
Laws of Electric Charges
Static electricity and the
development of
Technology
1. Like charges repel.
2. Unlike charges attract
3. Charges objects attract neutral objects
Lightning Rod: A metal rod or conductor attached to a building and
electrically connected to the ground. If lightning hits the building, it will
preferably hit the rod and the electricity will be conducted into the
ground instead of through the building
-
Static vs Current Electricity
Other examples: fabric softener, bounce sheets, electric eels!
Although static electricity is built up and does not move around, it
cannot be harnessed as a useful energy source. It cannot be used or
collected to run electrical devices. Current electricity can because it
can flow from one point to another
Ohm’s Law
Potential Energy
Stored energy in an object
Electric Potential Energy
The electrical energy stored in a battery; electrons have stored energy
and the ability to do work after they leave the battery
Electric Potential
Difference
Also known as “voltage”. The amount of electric potential energy
(stored energy)
AKA - Voltage
Volt
The SI unit for measuring electric potential difference – symbol is V
(Named after Alessandro Volta, Italian physicist who invented the
battery)
Electrochemical cell
Converts chemical energy into electrical energy stored in charges so
that we are able to use the energy. Commonly just called a cell.
Battery
A collection of electrochemical cells. Dry cells are batteries used in
flashlights and portable DVD players. Wet cells are used in cars and
motorcycles.
Electrode
The 2 terminals on a battery (positive and negative sides). Usually,
made of 2 different metals but can also be made of a metal and
another type of material. The electrodes sit in an electrolyte.
Electrolyte
A substance that conducts electricity. In a dry cell it is a moist paste; in
a wet cell, it is a fluid.
Electric current
The flow of charged particles in an electric circuit
Ampere
The SI unit for electric current. Symbol = A. It is defined as 1 coulomb
of charge passing a given point per second. Named after French
physicist Andre-Marie Ampere who looked at the relationship between
electricity and magnetism.
Electric circuit
A complete pathway that allows electrons to flow. Remember drawing
circuit diagrams…
Parts of an electric circuit
1. Source of electrical energy – electrochemical cell or battery
2. Conductor – the wire through which energy flows
3. Electrical load – a device that changes electrical energy into other
forms of energy. Examples would be light bulbs, motors, heaters
4. Controls/Switches – A device that turns the circuit on or off
Conductor
Allows electricity to flow through. In a circuit, the conductor is the
wire through which electricity flows
Circuit Diagrams
Diagrams that use symbols to represent the different components of
the circuit
Resistor
A resistor controls or limits the amount of current passing through a
circuit
Resistors are marked with colored bands. These stripes indicate the
resistance of the resistor.
Ammeter
An ammeter is a device used to measure the amount of current
passing through a circuit
Voltmeter
A voltmeter is a device that measures the amount of voltage (or
electric potential difference) that is in a circuit
Open switch
In a circuit, an open switch shows that there is a break in the path of
the electrons and the electrons cannot continue to flow. An open
switch exists when you turn OFF lights… you open the switch and
electrons can no longer get to the light bulb to give the bulb energy!
Closed switch
In a circuit, a closed switch shows that there are NO breaks in the path
of electrons. They are able to continue to flow. A closed switch exists
when you turn ON lights… there is a continuous flow of electrons from
the switch to the light bulb, allowing the light bulb to turn on.
Electrical resistance
Measured in Ohm and describes how a material can slow down the
flow of electrons and convert electrical energy into other types of
energy. It is the ratio of voltage to current.
Ohm
The SI unit for electrical resistance. The symbol is Omega -
Factors that affect
Resistance in a Wire
1. Length – longer = more resistance
2. Diameter – Smaller = more resistance
3. Type – Some wires offer more resistance than others. Copper is an
excellent wire for electricity because it offers very little resistance and
electrons can flow easily. Nichrome is a combination of nickel and
chromium and is a strong resistor!
4. Temperature – higher temperatures result in more resistance
because all of the electrons are erratic
Ohm’s Law
Ohm’s Law states that:
Resistance (R) = Voltage (V) or R = V
Current (I)
Resistance will be measured in Ohm (
I
)
Voltage will be measured in Volts (V)
Current will be measured in Amperes (A)