Transcript Current Electricity - Petoskey High School

Current Electricity
Comparing Electricity
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Static electricity is a build up of
electrons
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This creates attractions and repulsions
The electrons are held in place until
there is a discharge, then the electrons
move from one place to another
The movement of electrons is current
electricity!!
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Flowing electrons is current
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Current electricity can be AC (alternating
current) like wall outlets and ceiling lights
Current electricity can be DC (direct
current) like a bolt of lightning or from a
battery
In both cases, electrons are moving
from the negative end (more electrons)
to the positive end
Four Terms
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Four major terms associated with current
electricity are
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Voltage (potential difference) is the pressure
on the electrons to make them move
Current is the amount of electrons moving
Resistance is the push against the movement
of the electrons
Power is the work being done by the moving
electrons in a given time
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Think about electricity like a big
bucket of water
The more full the bucket, the
harder the water pushes out the
faucet – this push is voltage
The more the faucet is opened,
more water flows out – this flow
of water is current
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The faucet can be opened all the
way and make it easy for water
to flow, or it can be closed part
way and make it harder for water
to flow
The “harder to flow” is resistance
to flow of water – it also is the
resistance to flow of electricity
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The water coming out of the
faucet can spray, wash away dirt,
even turn a water wheel to make
electricity
All of these things are work
Measuring how much work is
done in a specific amount of time
is power
Electrical power is watts
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Conductors are materials that allow electricity
to flow through them
Good conductors, like copper wire, have low
resistance. This means that they will easily
allow electricity to pass through them
Conductors conduct because they hold
electrons loosely, and electrons can pass
from one atom to the next, and down
through the whole piece of material
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Insulators are materials the do not
allow electricity to pass through them
Insulators hold their electrons tightly,
so they can not be passed or moved
Voltage Sources
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Electricity coming from a battery flows from the
negative terminal to the positive terminal. It flows
directly from one to the other, in only one
direction.
Wall outlets have electricity that keeps changing,
or alternating direction. This means that the
electricity is moving forward through the wire,
then back, then forward again
This back and forth motion of electrons can still do
work, just as the back and forth motion of a saw
still cuts
Ohm’s Law
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There is a relationship between voltage,
current, and resistance
Think back about the water tank
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If there is not much water in the tank, there
will not be much current – regardless of how
much the faucet is opened.
If there is a lot of water in the tank, the faucet
controls how much water flows out.
The more resistance there is, the less current
Ohm’s Law Formula
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Voltage = current * resistance
Or
Current = voltage / resistance
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Hopefully this makes sense – if the resistance
increases, the current decreases!!
The formula is written V=IR
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V = voltage
I = current
R = resistance
Taking the measure
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Voltage or Potential Difference is
measured in Volts (V)
Current is measured in amperes or
amps (I)
Resistance is measured in ohms(R)
Power is measured in watts(P)
Practice
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What is the current of a 9 volt circuit
with 20 ohms of resistance?
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V=IR, or I=V/R
I=9 v/20 ohms
I=.45 amps
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What is the voltage of a circuit with 50
ohms of resistance and .01 amps?
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V=IR
V= .01 amps * 50 ohms
V= .5 volts
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What is the resistance of a 110 volt
circuit with 4 amps of current?
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V=IR, or R=V/I
R=110 v/4 amps
R= 27.5 ohms
Practice
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What is the voltage of a circuit with 10
ohms of resistance and 15 amps of
current?
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V=IR
I=15 amps
R= 10 ohms
V = 15 amps * 10 ohms
V = 150 volts
Practice
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What is the resistance of a 25 volt
circuit with 5 amps of current?
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R = V/I
V= 25 Volts
I= 5 amps
R = 25 Volts/5 amps
R = 5 ohms
Power
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Power is volts times amps
P=VI
Practice
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What is the power of a 5 volt circuit
with 15 amps of current?
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P=VI
P= 5 volts * 15 amps
P= 75 watts