Download Science 9 electricity powerpoint Topic 2

Unit D Section 2.0
Technologies can be used to
transfer and control electricity
2.1 – Controlling the Flow of
Electrical Current
• Electrical current flows through circuits
• The amount of current that can flow through a
circuit is limited by the conductive properties of
the components in the circuit
http://videos.howstuffworks.com/discovery/
27710-how-do-they-do-it-creating-neonsigns-video.htm
Conductors and Insulators
• In conductors, electrons can move easily
because they are not tightly bound to the nuclei
of the atoms
• In insulators, the electrons cannot move easily
• http://www.youtube.com/watch?v=8Pnsbh0DrE
4
Superconductors
• A superconductor is a material that have no
resistance to electron flow
• Many materials are superconductive at very low
temperatures
http://app.discoveryeducation.ca/search?Ntt=sup
erconductors
Using Conductors, Resistors &
Insulators
• Resistance is a measure of how difficult it is for
electrons to flow
• Resistance is measured in ohms (Ω)
• Resistors are parts of a circuit that provide
high resistance to reduce the amount of
current flowing through the circuit
• For any given voltage, more current flows
through a resistor with a LOW resistance
than one through with a HIGH resistance
• http://www.bbc.co.uk/bitesize/standard/physics/
using_electricity/resistance/activity/
Devices that use Resistors
• The more resistance a substance has, the more
the substance gains energy from each electron
passing through it.
• The energy gained is radiated to its
surroundings as either heat or light
• Some examples of devices that use resistors
are:
• http://www.youtube.com/watch?v=t4SP_mYh4
wQ
• HowStuffWorks How does a lie detector
(polygraph) work
Switches and Variable Resistors
• Switches create a break in the circuit that
interrupts current flow, therefore controlling
the flow of current in the circuit
• A variable resistor is another type of control
• These resistors (also known a rheostats) allow
you to adjust the amount of current flowing
through a circuit, rather than simply turning it on
or off
• This can be done through control knobs or
pedals
Topic 2.2 Modeling and
Measuring Electricity
Electrical Charge
• Electrical charge is measured in Coulombs
• This is named after Charles A. Coulomb
• 1 coloumb = 6.25 billion billion electrons
2.2 – Modeling and Measuring
Electricity
• Voltage is a measure of how much potential
energy each electron that flows through a
circuit possesses
• Voltage is related to both current and
resistance in circuits
Ohm’s Law
• In 1826, Georg Ohm
determined through
experiments that
voltage (V), current (I)
and resistance (R) are
mathematically related:
• Resistance is measured
in ohms (Ω)
V  IR
Ohm’s Law states that, as long as temperature
remains constant:
1. The resistance of a conductor remains
constant
2. The current is directly proportional to the
voltage applied
• http://www.youtube.com/watch?v=mHLvtGjum4
• MAKE presents: Ohm's Law
Applying Ohm’s Law
2.3 – Analyzing and Building
Circuits
• Circuit diagrams or schematics are
representations of a circuit that is built
• Recall that all circuits require four
components:
Parallel and Series Circuits
• Circuits can be divided into two general types:
parallel and series
• These circuit types are defined by the number
of branches that are present in the circuit
• http://www.bbc.co.uk/schools/gcsebitesize/scie
nce/add_aqa/electricity/circuitsact.shtml
Series Circuits
• Definition:
• Diagram:
the current passes through
each bulb in turn – there is only
one pathway
Parallel Circuits
• Definition:
• Diagram
have a separate path for each
section of the circuit
Effects of Multiple Paths in Parallel
Circuits
• In parallel circuits, adding more resistors in
circuits actually will reduce the overall
resistance of the circuit
• As well, the voltage change in each branch is
equal
Applications of Parallel and Series
Circuits
• Parallel circuits are more commonly used in
devices than series circuits
• Imagine what would occur if your house used
series circuits instead of a number of parallel
circuits…
Transistors
• In tiny consumer electronics, transistors are
used instead of conventional switches
• Transistors are made of three layers of silicon
sandwiched together
• These transistors have no moving parts and
operate on digital code running through the
middle layer of the transistor to control the
movement of current through a circuit
Microcircuits
• Are also called integrated
circuits
• Are made up of
microscopic transistors
and resistors
• It is a circuit on an
extremely small scale