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Electricity
Energy transfers
Energy transfers in everyday appliances
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Cards (24)
What is the relationship between the energy transferred from the mains and the power of an electric heater?
The
energy transferred depends
on the
power
and the
time
it
is
used.
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How much energy does a 1 kilowatt heater use in 1 hour compared to a 2 kilowatt heater?
A 1 kilowatt heater uses the same amount of energy in 1 hour as a 2 kilowatt heater does in
half an hour
.
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How does the energy usage of a 100 W lamp compare to a 3000 W heater?
A 100 W lamp uses the same amount of energy in
30 hours
as a 3000 W heater does in
1 hour
.
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What is the equation to calculate the energy transferred from the mains to an appliance?
Energy
transferred, E = power, P ×
time
, t
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What are the units for energy, power, and time in the equation E = P × t?
Energy
is in
joules
(J), power is in
watts
(W), and time is in
seconds
(s).
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What is the equation to calculate the power supplied to an electrical appliance?
Power
, P =
current
, I ×
potential difference
, V
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What are the units for power, current, and potential difference in the equation P = I × V?
Power is in
watts
(W), current is in
amperes
(A), and potential difference is in
volts
(V).
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How is the efficiency of an electrical device calculated?
Efficiency = (
output power
/
input power
) × 100
Output power is the
useful energy
transferred per second.
Input power is the total power
supplied
to the device.
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If an appliance has an input power of 2000 W and an efficiency of 80%, what is its output power?
Output power = 0.80 × 2000 W =
1600 W
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How can efficiency values be expressed?
Efficiency values can be expressed as a
ratio
or a percentage.
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What is the maximum percentage efficiency of an electrical appliance?
The percentage efficiency of an electrical appliance is always less than
100%
.
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What is the relationship between input power and output power in terms of efficiency?
Input
power
is the total power supplied to the
appliance.
Output power is the
useful
energy
transferred
per
second.
Efficiency indicates how much of the input power is converted to
useful
output.
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What is the primary purpose of everyday electrical appliances?
To bring about
energy transfers
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What factors determine the amount of energy an appliance transfers?
The time the appliance is switched on and its
power
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What happens when charge flows in a circuit?
Work
is done
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How can the amount of energy transferred by electrical work be calculated?
Using the
equation
: energy transferred =
power
× time
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What is the equation for energy transferred in terms of power and time?
E = Pt
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What is the equation for energy transferred in terms of charge flow and potential difference?
E = QV
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What are the units for energy transferred, power, time, charge flow, and potential difference?
Energy transferred:
joules
(J), power:
watts
(W), time:
seconds
(s), charge flow:
coulombs
(C), potential difference:
volts
(V)
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What is the unit of energy transferred?
Joules
(J)
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What is the unit of power?
Watts (W)
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What is the unit of time?
Seconds
(s)
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What is the unit of charge flow?
Coulombs
(C)
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What is the unit of potential difference?
Volts (V)
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