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Energy
Changes in energy calculations
power & work done
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Created by
Marwa Jbara
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Cards (29)
What is the focus of today's video?
Understanding and calculating
power
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How many definitions of power are there?
Two
definitions
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What is the first definition of power?
Rate at which
energy
is
transferred
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What is the equation for power based on energy transferred?
Power
=
Energy transferred
/
Time
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What is the second definition of power?
Rate
at which
work
is
done
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What is the equation for power based on work done?
Power
=
Work done
/
Time
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How is work done defined in this context?
Energy
transferred using a
force
over distance
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If you push a car down the road, what is the energy referred to as?
Work done
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How is electrical energy transferred from a plug socket described?
As
energy transferred
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What unit is power measured in?
Watts
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What units are energy transferred and work done measured in?
Joules
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What unit is time measured in?
Seconds
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How do you compare the power of two lamps?
Use the
energy transferred
equation
Calculate power for each lamp
Compare the results
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How much energy does the left lamp transfer?
1200
joules
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How long does the left lamp take to transfer energy?
20
seconds
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What is the power of the left lamp?
60 watts
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How much energy does the right lamp transfer?
1500
joules
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How long does the right lamp take to transfer energy?
30 seconds
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What is the power of the right lamp?
50
watts
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How do you find the energy transferred by a microwave?
Rearrange the
power
equation
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How long is the microwave on for in seconds?
180
seconds
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What is the energy transferred by an 1100 watt microwave in three minutes?
198,000
joules
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How do you convert joules to kilojoules?
Divide by
1000
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How much energy is transferred in kilojoules?
198 kilojoules
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How much work is done to push a car down the street?
9
kilojoules
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How long does it take to do the work on the car?
20 seconds
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What is the power used to push the car?
450
watts
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What are the key equations for power?
Power
=
Energy transferred
/ Time
Power =
Work done
/ Time
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What are the units for power, energy, and time?
Power:
Watts
Energy:
Joules
Time:
Seconds
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