Download The Control of Electricity in Circuits

The Control of Electricity in
Circuits
10.2, 10.3 and 10.5
Read 10.2 together before copying notes
10.2 Electricity and Electric Circuits
• Remember our discussion about static electricity
and what happens when you touch a doorknob?
• The shock you experience is caused by the flow
or movement of electric charges between you
and the doorknob.
• This flow of electric charges is known as
electric current.
An Electric Circuit
• There is one very important difference
between a static electricity discharge and
the electric current flowing through a light
bulb.
• The current flowing through the light bulb
is flowing in a controlled path called an
electric circuit.
Parts of an Electric Circuit
• All electric circuits have the same four basic
parts:
– Source of electrical energy
– Electric load
– Electric circuit control device (switch)
– Connectors
Source of Electrical Energy
• The electrons need to be supplied from a source.
• The power source can be:
– a battery
– a power outlet in your home or school
– a car battery
– a generator
– a photoelectric cell or many other alternatives
Electrical Load
• The electrical load is actually the reason the
electric circuit exists.
• It is the thing that requires the electrical energy.
• More familiar electrical loads include:
–
–
–
–
–
light bulbs
televisions
computers
toasters
DVD players
Electric Circuit Control Devices
• As the name suggests, this is a device for
controlling an electric circuit.
• You know these devices as switches.
• They can be simple like a light switch or the
switch on a computer.
• Other switches can be more sophisticated like the
timer on a VCR or a microwave oven.
Connectors
• Connectors are the conductors that allow the
electric current to flow from point A to point B.
• The most common connectors are wires, which
come in all different shapes and sizes.
• The purpose of connectors is to provide a
“controlled path” through which the electric
current can flow.
A Typical Circuit
Electrical Load
Connectors
Energy Source
Circuit Control
Device
Closed Circuits and Open Circuits
• Circuits can only exist in two possible
states:
– Closed circuits are those circuits which are
operating and current is flowing.
– Open circuits are those circuits in which current
is not flowing; usually because the switch is not
closed.
How do we draw a circuit?
• To simplify the drawing of electric circuits,
a special set of symbols is used.
• Drawings of circuits using these symbols
are called schematic circuit diagrams.
Electrical Symbols
Electrical Diagrams & Schematics
Homework
• Page 301# 3 - 5, and 7.
10.3 Electric Potential (do not copy)
Gravitational Potential
GAS
Chemical
Elastic Potential
Potential
Energy
Potential Electrical Energy
• Why is it safe to touch a 1.5 volt battery at both
ends but it is not safe to touch two wires
sticking out of a 120 volt outlet?
• In both cases, you are completing a circuit, but
in the case of the 1.5 volt battery, the amount of
energy each electron has is much less than that
of the electrons leaving the outlet.
• The amount of potential energy is higher in the
120 volt outlet.
Potential Electrical Energy
• The potential energy of a power source is very
important to consider.
• The greater the potential energy of a power
source, the greater the force applied to the
electrical load in the circuit.
• This is why a 1.5 volt battery will not light a 60
watt bulb. The electrons leaving the battery do
not have enough energy to create light.
Potential Electrical Energy
• The energy each electron has is called the
electric potential of the electron.
• Electric potential is commonly called voltage.
• The common unit of measurement of electric
potential is the volt.
• The symbol of the volt is V.
• Table 1 p.303 shows some sources of electric
potential and their voltage values.
Questions
• P.303 #1,2 & 3
Answers
• 1 – if the electrons weren’t in constant motion
then the electricity would not be flowing
• B – electrons flow out of the negative terminal,
around the circuit and back into the positive
terminal
• 2 – electric potential is how much energy each
electron may have
• B – the (standard international, SI) unit for
measuring voltage is the volt and the symbol is
capital V
Answers
• 4 – in a 6V source, the voltage provided by
each electron is not as great as in a 120V
outlet; each electron does not have as much
potential energy and therefore, you don’t
notice it as much as you do in a greater
source
Pop-Quiz
Take out one sheet of loose-leaf…put away
notes/textbooks…number from 1-10…put
your name and today’s date at the top.
Pop-Quiz Questions
•
•
•
•
•
1.
2.
3.
4.
5.
Name the 4 essential parts of a circuit.
Tell what each part of the circuit does.
Give one example of each part of a circuit.
What are schematic diagrams?
Who could use a schematic diagram?
Pop-Quiz Questions
• 6. Draw one symbol we used on the sample
schematic diagrams in your notes. (eg. Cell)
• 7. What’s the difference between static and
current electricity?
• 8. Describe what an open circuit would look
like.
• 9. Would a light bulb light up in an open circuit?
• 10. What is electric potential measured in?
Swap papers!
Have someone else correct your
answers and put a mark out of 10 at
the top.
Quiz Answers
• 1. 4 parts: power source, load, control device and
connectors.
• 2. power source provides energy, load is what is
being run by the energy, control device is the
switch and it turns the circuit on/off and
connectors are usually wires.
• 3. power source = battery, load = iPod, control
device = on/off switch and connectors are the
wires inside
• 4. schematics are diagrams of
circuits/wiring that use symbols instead of
actual pictures
• 5. electricians would use schematics
• 6. see p.300 or 545
• 7. static electricity sits still and current
electricity flows
• 8. an open circuit would show the switch
open or there would be a break in the circuit
• 9. a light bulb would not light up in an
open circuit because the electricity can’t
flow
• 10. electric potential is measured in volts
• Record a mark out of 10 and then hand
them in.
10.5 Electrochemical Cells
• Cell is another name for battery.
• Cells are classified as either primary or
secondary.
• In a primary cell, chemical reactions use up
some of the materials in the cell as electrons
flow from it.
• When these materials have been used up, the
cell is said to be discharged and cannot be
recharged.
Electrochemical Cells
• Unlike primary cells, a secondary cell can be
discharged and recharged many hundreds of times.
• Secondary cells are often referred to rechargeable
batteries.
• Secondary cells are so named since there are two
chemical processes involved:
– one to discharge the cell
– one to charge the cell
• A car battery consists of a group of secondary
cells.
Primary Cells
• Primary cells can be further classified as either
wet or dry.
• The primary wet cell was first developed in
1800 by Italian scientist, Alessandro Volta.
• This cell is therefore called the voltaic cell.
Primary Wet Cells
• A wet cell is made up of two pieces of metal
that are placed in a liquid.
• The metal plates, usually zinc and copper, are
called electrodes.
• The liquid in the cell is called the electrolyte.
• An electrolyte is any liquid that conducts an
electric current.
Primary Dry Cells
• The dry cell is similar to the wet cell, but the
electrolyte is a moist paste instead of a liquid.
• A group of cells make up a battery.
Questions
• P.307 # 1,2 and 3