The document discusses key concepts in current electricity including: 1) Current is defined as the flow of electric charge through a medium. Resistance and potential difference affect the current in a circuit. 2) Basic circuit components like batteries, lamps, switches and wires are introduced along with common circuit symbols. 3) Experiments with simple series and parallel circuits are described to demonstrate the relationships between current, resistance, and potential difference. Kirchhoff's laws and definitions of electrical power are also covered.

1. V
Current Electricity
Introductory Physics
Canadian Academy
Group Members: Kaiya Yamada

2. Current Electricity Construct and explain.
Work in pairs or by yourself for these tasks.
With each question:
• Build it in the PhET simulation
• Build it in the lab if possible
• Draw the circuit diagram and
answer the questions on the slide.
You should be able to:
http://phet.colorado.edu/en/simulation/ • Define current electricity
circuit-construction-kit-dc • Define resistance and state the factors that
affect resistance in a metal wire
• Define potential difference (voltage)
Your finished work should be • Explain the effect of potential difference
uploaded to SlideShare (or and resistance on a current
Google Docs if it works) and • Draw basic circuit diagrams involving
batteries, lamps, switches and wires
embedded into a blog post.
• Define electrical power including the
relationship to voltage and current

3. Some basic circuit symbols
You can use these to build the circuits on the next slides.
wire cell battery
junction
+ - + -
cathode anode
electron flow
bulb/ lamp resistor
conventional current
What do these two components measure?
switch
V A
voltmeter ammeter

4. A simple series circuit
Build this circuit.
Define current electricity.
• a flow of electric charge through a medium.
Current electricity is the movement of electrons through materials and is
therefore a transfer of charge. It can be contrasted with static electricity,
conventional current which can be said to be electricity held by a material with electric charge.
electron flow
A Label the direction of flow of electrons and the direction of the
conventional current.
What is the difference between them?
They are opposite in direction. The conventional current direction is from
plus to minus around the circuit. It is indicated by the green arrow.
Electrons flow the other way. They are negatively charged, so they are
repelled by negative charge and pushed out of the negative terminal. It is
indicated by the red arrow.
Use the non-contact ammeter to measure the current in the circuit.
• 0.90 amps
What happens if the cell is not included in the circuit? Explain.
• If the cell is not included in the circuit, the circuit will not work
because there is no source for electricity. Without electricity, the
bulb would not light and the ammeter would indicate 0 amps.

5. Switches and current
Build this circuit.
Measure the current with the switch in the open position.
• 0 amps
Close the switch and measure the current. Explain your answer.
• 0.9 amps
• This happens because when the current is in the open
position, the circuit is broken and the electricity can not
A flow. However, when the switch is closed, the circuit is
also closed so the electricity can flow through and light
the bulb and change the reading on the ammeter to 0.9
amps.
Move the ammeter to different positions in the circuit and
measure the current. Does position matter?
• No, it does not. Charge is not destroyed so the current
strength will be the same anywhere.
Are electrons ‘created’ in the cell?
Electrons are not created in the cell. An imbalance in the electrons in the
cell caused by chemical reactions in the battery make the electrons flow
Are electrons ‘used up’ in the circuit? around the circuit back to the cell. The chemical reactions in the cell make
the existing electrons move towards one side of the cell which is the anode.
No, they are not. They keep flowing Because of the imbalance between one side of the battery having a heavy
until they arrive back at the source. concentration of electrons and the other side lacking this, the electrons try
to spread out and diffuse the concentration. However, the battery prevents
The energy of the electrons is used up the electrons from going directly from the anode to the cathode. This and
and changed into heat and light. The the repulsion force between each electron causes the electrons to flow
around the circuit back to the cell.
electrons return to the cell.

6. Potential Difference (voltage)
Modify the circuit to increase the potential
difference by including two, then three, cells.
What happens to the bulb?
• The bulb’s brightness increases as we add
more bulbs. Too many cells cause the bulb to
burst.
Measure the current and potential difference.
A Cells Current (A) Potential Difference (V)
1 0.9 9.00
2 1.8 18.00
3 2.7 27.00
Define potential difference (voltage).
• the difference in electric potential energy per unit charge
V between two points.
Explain your results.
• Each time I increased a battery, the current increased by
Complete the circuit 0.9 amps and and the voltage increased by 9 volts. That
diagram for three cells. means that each battery has 0.9 amps and 9.00 volts
worth of power. Basically what we see is that when we
double the current, we double the energy difference.

7. Resistance (incandescent bulbs or lamps)
Go to the following applet and see resistance at a molecular level and how a light
bulb works.
http://micro.magnet.fsu.edu/electromag/java/filamentresistance/
Explain in your own words how moving charges cause a bulb to glow. What energy
transfers and transformations are taking place?
When a bulb is connected to a battery, first, potential chemical energy is converted to
electrical energy, and current flows from one contact to another through wires and a
filament. As electrons move along the filament, they bump into atoms that make up
the filament. There is a transfer of energy. The energy of each impact vibrates the
atoms. Basically the current heats the atoms up. Here, electrical energy is transferred
into heat energy. If the filament is thin or made of a certain material, it will heat up
more easily because it is more resistant to the flow of electrons. The electrons in the
vibrating atoms can be boosted to a higher energy level. When they return to their
normal level, they release energy in the form of photons. Here, electrical energy is
transferred into light energy.
Explain what has happened when a cell (battery) has run out.
When a battery runs out, all the chemicals that mix to cause
the imbalance in the electrons run out. This means that the
imbalance of electrons will not be created anymore. Therefore,
no more current will flow from the battery unless it is
recharged (if it is rechargeable)

8. Resistance (incandescent bulbs or lamps)
Build this circuit.
Add bulbs and record your observations.
Bulbs Current (A) Observations
1 1.8 The bulbs seem to getting
2 0.9 dimmer and dimmer as I
A increase the number of
3 0.6 bulbs. The number of amps
4 0.45 is decreasing with each
5 0.36 reading as well.
Explain your findings in detail.
The current flowing through the circuit with just one bulb is 1.8 amps. The current flowing through the circuit
with two bulbs is 0.9 amps. The current flowing through the circuit with three bulbs is 0.6 amps. From these
results, we can see that the number of amps is originally 1.8 amps and from there it becomes one half, one third,
etc. This means that the numbers of amps flowing through this circuit is 1.8 amps divided by the number of bulbs.
Remove all the bulbs to create a
circuit and measure the current. Explain.
The number of amps flowing through the circuit drastically increases to 12260.87 amps and the light bulbs catch
on fire. Because the current electricity is not being used up anywhere as there is no load, the charge keeps
building up showing the high amp count. Heat builds up in the circuit and can cause a fire.

9. Conclusions Use your findings in the circuits so far to write your own Laws.
Law of current in a loop.
“This is just a statement of energy conservation. As a current flows through
resistors in a circuit, potential drops. The sum of the potential drops is the
same as the supplied potential.”
Law of voltage and current. (what’s the relationship?)
“The relationship between the two values is direct. As voltage increases,
current increases at the same rate. E(voltage)=I(current)R(resistance) “
Law of resistance and current. (what’s the relationship?)
“The relationship is indirect. As the resistance is increased, the current speed
decreases. As the resistance is decreased, current speed increases. The
equation is resistance = potential difference/current. “
Why is it dangerous to have too little resistance in a circuit?
When there is too little resistance in a circuit, the charge or current builds up
without being used. This buildup causes the circuit to heat up. This can cause a
short circuit, which can lead to fires.

10. Parallel Circuits How many different routes can current take through this circuit?
• The current can take two different routes if the switches are
closed.
Close the lower switch only.
Observe the bulb and measure the current.
• The lower bulb lights up very brightly and the ammeter
shows that the current is 1.80 amps. The upper bulb does
not light up and the upper ammeter shows the current is 0
amps.
Close the upper switch only.
Observe the bulb and measure the current.
• The upper light bulb shines very brightly and the upper
ammeter shows the current is 1.80 amps. The lower bulb
does not light up and the lower ammeter shows the current
Draw a circuit diagram for is 0 amps.
this set-up below: Close both switches. Observe the bulbs and measure the current at
different positions.
• Both light bulbs light up. They are just as bright as the bulbs in
the cases above. Each ammeter shows the current is 1.8 amps.
The power supply fixes the potential difference, so each
component has the same potential difference across it.
Observe the animation carefully.
What happens to the electrons at junctions?
• The group of electrons split up in half. Half of them go one way
and the other half goes the other. The one half goes through the
lower branch and the other half of the electrons travel through
the upper branch. At the other end, the electrons come back
together. Because of the idea of conservation of charge, we can
understand that the total current flowing out of a junction is the
same as the total current flowing in.

11. Law of Parallel Circuits Write your own Law, based on observations.
Law of parallel circuits.
“The parallel circuit has more than one path for current
to flow. The same voltage is applied in each branch. If
load resistance in each branch is the same, the current
in each branch is the same. “
Now test your Law using a third bulb in parallel.
Draw the circuit diagram below and write your observations of the bulbs and of current.
The number of amps flowing through each
part of the circuit is still the same: 1.8 amps.
The brightness of each light bulb has not
changed either.

12. More Parallel Circuits Close one switch at a time and record your observations.
• By closing the lower switch, the bottom circuit is completed. The
bottom circuit has two light bulbs so the bulbs only glow half as
bright as with just one bulb. Also, the number of amps that is
shown is half of the previous 1.80 amps which is 9.00 amps.
• By closing the upper switch, the upper circuit is completed. The
upper circuit has one light bulb so the bulbs glow twice as bright
as the bulbs in the lower circuit. The upper ammeter also had an
amp count twice that of what was shown on the lower ammeter:
1.80 amps.
Close both switches and record your observations.
• The same observations can be made as those made above. They
are just happening at the same time.
Draw a circuit diagram for Carefully observe the junctions.
What is happening? Explain with reference to resistance and junctions.
this set-up below: • Because there are more light bulbs in the lower circuit, the
resistance is twice as great as the resistance in the upper circuit.
Therefore, the number of amps in the lower circuit is half that of
the upper circuit and the electrons are travelling a lot
slower(approximately half the speed) through the lower circuit
than they are through the upper circuit. This also means that for
every electron that goes through the lower branch with two light
bulbs, two electrons travel upwards through the upper branch.
This also means that for every electron that leaves the lower
branch to go back into the main circuit stream, two electrons
leave the upper branch back into the main electric circuit stream
back towards the cell. We also, of course, have to understand that
the sum of the current leaving each junction is the same as the
sum of the current entering each junction.
Do you need to modify your Law of Parallel Circuits?
Yes, I do.

13. Law of Parallel Circuits Modify your Law.
Law of parallel circuits.
“The parallel circuit has more than one path for current
to flow. The same voltage is applied in each branch. If
load resistance in each branch is the same, the current
in each branch is the same. If the load resistance in
each branch is different, the current in each branch will
be different. Also, if one branch is broken, current will
continue to flow through the other branch. “

14. More Resistance
Use two cells and two bulbs in a circuit. Use CTRL-click to adjust the resistance of the
bulbs (one is 20 ohms (Ω), the other is 10Ω).
What is the difference between these two bulbs on a molecular level?
• The electrons are moving a lot more slowly through the light bulb with the higher
resistance. The number of particles interfering with the electrons’ passage is
greater in the higher resistance light bulb.
Wire up the bulbs in two different circuits: series and parallel. Draw the circuits below.
Under each circuit, record and explain your observations.
Series: Parallel:
In this parallel circuit, the
lower branch had a light bulb
with a resistance of 20 ohms
and the upper bulb had a
resistance of 10 ohms. The
bulb with the lower
resistance shone much
In this series circuit, the brighter and the ammeter
ammeter showed that the showed that its current
current was 0.6 amps. The which was 1.80 amps was
bulbs were a bit dim, but they twice that of the lower
branch which was 9.00 amps.
were the same brightness.

15. Electrical Power
Define electrical power and state its unit.
• The rate at which electric energy is converted to other forms of energy such as
heat, light, and kinetic energy. The unit is the watt.
What is the relationship between electrical power and ‘power’ as we have studied in the previous
unit?
• In the previous unit, we defined power as the rate at which work is done. One equation
for power was Power=work/time. With electrical power, the concept is basically the same.
Electrical power is the rate at which electrical energy is supplied to a circuit or consumed
by a load. Equations for it would be Power=work done on charge/time or Power= energy
consumed by load/time.
Compare two methods of generating electrical power: one fossil-fuel based and one renewable. How do they work? What are
the benefits/ disadvantages of each?
Coal is a fossil fuel that is burned to boil water, which causes steam, which turns turbines. The spinning motion of the turbines
causes the electromagnets to generate electricity. This electricity is stored and sent out. There is a limit on this, however,
because coal is a fossil fuel and there are only so many fossil fuels in the world. It is a non-renewable energy source.
Wind power is a renewable power source and it works a bit differently. Wind power uses turbines as well. The wind turns the
turbines and produces electricity.
Advantages/disadvantages:
Advantages of coal: Coal has a very high energy density (a great deal of energy is released from a small mass of coal). It is
relatively easy to transport and cheap compared to other energy sources. It can be used directly in the home to provide heating.
Disadvantages of coal: Coal produces pollution and acid rain. Coal also gives off green house gases. The extraction of coal can
damage the environment. Coal is non-renewable. Coal-fired power stations need a large amount of fuel.
Advantages of wind energy: It is a cleaner energy source(no harmful chemical by-products), renewable, and free (of course the
turbines are not free, but the wind is).
Disadvantages of wind energy: It has low energy density(a large area would be needed for a great amount of energy). It is
unreliable as sometimes the wind does not blow. Wind turbines can also be very noisy and expensive to produce. They need a
large amount of land.

16. Extension
If you finish with extra time:
• Check the Laws you have written against published information. Do they concur?
• Find out more about circuits and their components.
• Find out about the difference between AC and DC.
• Build your own circuits and draw the circuit diagrams below.
I did check the laws I wrote and they do concur with published information. I reread
Kirchhoff’s first and second law. I learned them in grade 7, but it was a good review. I
have studied circuits a lot as I am interested in electricity. I used to love doing
experiments with static electricity and balloons and using it to bend water and make
pictures. I like how it is used to paint cars and in photocopying. DC is direct current.
It flows in only one direction. AC is alternating current. It constantly changes
direction, going first one way and then the other. I don’t have time to build and draw
circuits, but I did many at my old school. I liked using all the symbols for fuses, circuit
breakers, meters, etc.

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