Transcript 10.2,10.3 and 10.5 Notes & Activities

The Control of Electricity in
Circuits
10.2, 10.3 and 10.5
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
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
– Connectors
Source of Electrical Energy
• All circuits require a power source.
• The power source can be:
– a battery
– a power outlet in your home or school
– a car battery
– a generator
– a photoelectric cell
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:
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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” for the electric current to 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 simply 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, questions 1-5,7
10.3 Electric Potential
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 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 & 5
Homework Answers
1. It is necessary for electrons to continuously move
around the circuit to keep the energy flowing
which then keeps the “appliance” working. If the
electrons didn’t continue to flow, the load would
not receive energy and wouldn’t run.
b) The charge builds up at the negative terminal
and then flows out into the circuit. This happens
because the electrons have potential energy as
soon as the cell is created and they build up due
to the chemical reaction that occurs inside.
Homework Answers
2. Electric potential is the amount of energy
that each electron has.
b) The SI unit (International Standard Unit
of Measure) is the Volt
5. Answers will depend on appliances you
chose…discuss some of the answers
found.
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
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1.
2.
3.
4.
5.
Name the 4 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 would 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 at your group
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
discharged.
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