Download Electricity Ohms, Power 2013

Voltage
•the measure of energy
•measure of “potential difference
The unit for voltage is volts (V)
Potential difference flows from high energy to low energy
The potential difference (voltage) is 1.5 V for a battery.
The higher the energy, the greater the voltage
(potential difference).
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Current
is the rate of the flow of an
electrical charge.
How fast (speed) is
the electricity flowing
through these wires?
CURRENT (I) is measured in Amperes or Amps (A).
How fast is this water coming out?
+
2
The slowing down or stopping of current.

Resistance (R) is measured in ohms.
3
Match the word on the left to the phrase on the right.
Resistance
(R) in Ohms
How Fast?

Current
How much?
(I) in Amps
Voltage
(V) in Volts
How much is it slowed
down?
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Electrical Measuring
Instruments
• Voltmeter-used in parallel to
measure voltage
• Ammeter-used in series to measure
current
• Galvanometer-used to detect a
current
• Ohmmeter-measures resistance
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Georg
Simon
Ohm
We can use this formula to figure out
voltage, current and resistance.
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Ohm’s Law Information
• If voltage goes up, the charges move a little
faster between atoms and we get more
current.
•A current vs. voltage graph shows us if
resistance changes.
•Resistance of metals increases with
temperature, because the particles collide
more often causing more resistance.
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Calculating Ohms Law
I=V/R
So, to find Current, we need to
divide voltage by resistance.
V
volts
I
amps
Divide
R
ohms
Multiply
I=V/R
And, to find Resistance, we
need to DIVIDE voltage by
current.
R= V
I
To find voltage we multiple
current and resistance. V = IR
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Calculate the potential difference (voltage)
across a 3  resistor if a 0.5 A current is
flowing through it.
I=V/R
What do you know?
V = 0.5 A x 3 
V=?
I = 0.5 A
R= 3
V = 1.5 Volts
9
A radio with a resistance of 240  is
plugged into a 120 V outlet. What is the
current flowing from the outlet?
I=V/R
What do you know?
V = 120 V
I= ?
R = 240 
I = 120 / 240
0.5 amps = I
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Do the Practice Problem
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Electrical Power
is rate at which energy flows
Power (P) is measured in Watts (W)
Power = current x voltage
P=IxV
Divide
P
watts
I
amps
So, to find Current, we need to
DIVIDE power by voltage.
I= P
V
V
volts
Multiply
And, to find Voltage, we
need to DIVIDE power by
current.
V= P
I
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Where do Power Units come from?
Power
Joules
second
(Watts)
= Voltage
=
Joules
Coulomb
(volts)
x Current
x
Coulomb
second
(amps)
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Electrical Power Problem
If a CD player uses 4.5 V with 0.2 amps of
current, what is the power it uses?
P= I x V
P= ?
I = 0.2 A
V = 4.5 V
P = 0.2 A x 4.5 V
P = 0.9 Watts
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Do the Practice Problem
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Electrical Energy
Is measured in kilowatt-hours
Kilo means 1000x
Electrical Energy = power x time
E=Pxt
Divide
E
kWhr
P
kW
t
hr
Multiply
So, to find power, we need to
DIVIDE energy by time.
P= E
t
And, to find time, we need
to DIVIDE energy by power.
t= E
P
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Electrical Energy Problem
• You use your hairdryer for 10 minutes
everyday. The hairdryer uses 1000
watts. How many kilowatt-hours does
your hairdryer use in 12 days?
E=Pxt
E = 1 kW x 0.17 hr
E=
0.17 x 12 days= 2 kWhr
P = 1000 W = 1 kW
t = 10min / 60 = 0.17 hr
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Do the Practice Problems
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