Transcript Electric Current - Physics with Mrs. Allen

There are two requirements that must be met
in order to establish an electric circuit
1. There must be an energy source
(battery) capable of doing work on
charge to move it from a low energy
location to a high energy location. This
establishes a potential between the two
ends of an electric circuit.
2. There must be a closed conducting loop
that connects from the high potential to
the low potential.
The flow of electric current is
dependent on a difference of potential
between two points
 If there is no difference, there is no
flow
 Current is the rate at which a charge
flows past a point on a circuit
 Current flows from the negative
terminal to the positive terminal
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The current in a light bulb is 0.835 A. How
long does it take for a total charge of 1.67 C
to pass a point in the wire?
Q
I
t
Q 1.67C
t 

 2.00s
I
0.835A
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A hair dryer draws a current of 9.1 A. How
long does it take for 1.9x103C of charge to
pass through the hair dryer?
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Light a bulb, spin a motor, listen to music
Considered a load
The rate at which energy is consumed (used)
by a load is called power
Recall from last semester that power is a rate
of doing work
Similarly, electrons are now doing work
Electric power is the rate at which energy is
consumed
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A 6.0 V battery delivers a 0.50 A current to an
electric motor connected across its terminals.
If the motor runs for 5.0 minutes, how much
electric energy is delivered?
Power companies actually sell energy
 A kilowatt is equal to 1000 W
 Power companies sell energy in large
quantities called the kilowatt hour
 A kilowatt hour is equal to 1000 W
delivered over 3600 s (1 hour) or 3.6 x
106 J
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To calculate cost:
1. Determine the power in
kilowatts
2. Determine energy consumed by
multiplying power in kilowatts
by time in hours
3. Multiply the kilowatt hour by
the cost for each kilowatt hour
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A 60 W light bulb is connected to a
120 V power source. The power
company charges $0.11 per kWh.
◦ What is the current through the light
bulb?
◦ How much would it cost to keep the
bulb lit for two hours?
E  Pt
TotalCost  energyxcost
E  Pt  0.060kWx 2h  0.120kW  h
Total  0.120kW  h($0.11/ kW  h)  $0.013  1.3cents