Download Voltage

The flow of electrons
M Tommasi
4/30/2017
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Electric current
Static electricity is the……..
The flow of e- in a wire is called an electric
current
More e- implies greater current.
It is measured in Amperes (amps)
The symbol is the letter “I”
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Resistance
It is the opposition to the flow of electrons.
It is what makes some wires better
conductors.
It changes electricity into light or heat
It is measured in ohms
The symbol is “R”
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Voltage
To move object we need to push them
Electrons can be pushed also
That push is called voltage
The bigger the push the higher the voltage
It is measured in volts
The symbol is “V”
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Donow
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Give an example of a load.
What does a switch do to a circuit?
What is the main difference
between a series and a parallel
circuit?
Draw a series circuit containing a
power source, a switch and 2
loads?
What happens in a series circuit
that contains a power source, a
switch and 2 light bulbs if one light
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bulb blows out?
Reviewing
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Current (I) is the flow of
electrons in a circuit
Voltage (V) is how hard the
electrons are pushed
Resistance (R) is the
“friction” of electric flow.
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Possibilities
Can you have
 A) high current and high voltage?
 B) high current and low voltage?
 C) low current and high voltage?
 D) low current and low voltage?
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Ohm’s law
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A locomotive can push a train of cars
against friction at a velocity.
If there’s a lot of friction it can push only a
few cars
To push a lot of cars it has to push harder
The amount of push a locomotive can
provide depends on the friction and
number of cars.
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Ohm’s law
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In electricity voltage is the
locomotive
The voltage equals the
current x resistance
V=IxR
If there’s more resistance you
have to push harder
If you want to move more
electrons you have to push
harder
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Problem 1
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A voltage has to push
electrons through a load or
resistor
Problem: What voltage is
needed to push a current of
5 amps through a light bulb
that has a 4 ohms
resistance inside it?
V=IxR
V = 5 x 4 = 20 volts
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Question 2
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What is the current going through a wire
that has a resistance of 30 ohms if the
voltage pushing the electrons is 45 volts?
V=IxR
45 = I x 30
I = 45/30
I = 1.5 ?
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Donow
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What is voltage?
What is current?
What is resistance?
What voltage is necessary to push
3 amps of current through a 4 ohm
resistor?
What current can go through a 5
ohm resistor if 4 volts are pushing
it?
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Electrical power
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The power needed to run an
appliance depends on the voltage
and the current
Every appliance needs a different
amount of power to work
Power = voltage x current
P=VxI
In the US the voltage in any
regular outlet is always 120 volts
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Example
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How much power is used by a light
bulb if the voltage across the light
bulb is 120 V and the current going
through it is 2 amps?
P=VxI
P = 120 x 2 = 240 watts.
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example
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What power is being used by a hair
dryer if the current going through it
is 10 amps?
Power = voltage x current
Power = 120 x 10
Power = 1200 watts
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Two types of current
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Electrons can be pushed in 2 different
ways
They can be pushed out directly from
one point and go into another (DC or
Direct Current)
The electrons can be made to go back
and forth (AC or Alternating Current)
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Creating DC (direct current)
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DC can be created in several ways
1) wet cell-using liquid acid and two different
metals to chemically release electrons
Car batteries are a kind of wet cells
2) dry cell-using an acid paste instead of
liquid acid to release electrons
These are the regular “batteries”
Cells always have a voltage of 1.5 V
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Creating a DC current
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3) battery- a group of cells working
together
That’s a 9-volt battery
4) Solar cells- pure silicone sheets that
use sun light to push electrons
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Creating (AC) alternating current
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A magnet is moved back and forth
near a wire
As the magnet moves the electrons
are pushed back and forth
The current changes direction
In the US the current changes
direction 60 times a second (60 Hz)
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Creating alternating current
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AC current is made by
blocking a river (Dam) and
allowing the escaping water to
turn a turbine (hydroelectric).
Or by boiling water and letting
the steam turn the turbine
The heat to boil the water can
be made by burning coal, oil
or nuclear power.
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Electrical safety
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Never handle an appliance with wet hands or
while standing in water
Never run wires under a carpet
Don’t connect too many appliances to the
same circuit
Get rid of extensions if they are damaged
Never stick metals inside electrical
appliances
Never come too close to fallen power lines.
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