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Unit 2: Electricity
2.4 Energy Transfers in Electrical Appliances
2.4.1 Power
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What is the definition of power?
The rate of energy transfer
Power is measured in
watts
One watt is equivalent to one joule per
second
.
What is the formula for calculating power using voltage and current?
P
=
P =
P
=
V
I
VI
V
I
In the formula
P
=
P =
P
=
V
I
VI
V
I
, the variable
V
V
V
represents voltage
In the formula
P
=
P =
P
=
V
I
VI
V
I
, the variable
I
I
I
represents current, measured in amperes.
Match the power formula with its variables:
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
↔️ Energy, Time
P
=
P =
P
=
V
I
VI
V
I
↔️ Voltage, Current
What is the unit for voltage in the power formula
P
=
P =
P
=
V
I
VI
V
I
?
Volts
The formula
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
uses the variables energy and time
If a device operates at 12 V and draws 2 A, what is its power consumption?
24 W
What is the unit of power?
Watt
The current is measured in
amperes
The formula for power using energy and time is P = \frac{
E
}{t}</latex>
Match the formula with its variables and units:
P
=
P =
P
=
V
I
VI
V
I
↔️ Voltage, Current, W = V*A
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
↔️ Energy, Time, W = J/s
What is the power consumption of a device operating at 12 V and drawing2 A?
24 W
To calculate power using voltage and current, the formula is
P = VI
The formula
P
=
P =
P
=
V
I
VI
V
I
is derived from the definitions of voltage and current
What is the unit of voltage?
Volt
Arrange the variables in the correct order for the formula
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
1️⃣ Energy
2️⃣ Time
3️⃣ Power
What are the units for energy and time in the formula
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
?
J and s
In the formula
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
,
E
E
E
represents energy
Match the variable with its symbol and units:
Power ↔️
P
P
P
, Watts
Energy ↔️
E
E
E
, Joules
Time ↔️
t
t
t
, Seconds
What is the power of a light bulb that transfers 600 joules of energy in 30 seconds?
20 W
1 watt is equal to 1 joule per
second
What is the definition of a watt?
Joule per second
To calculate power using voltage and current, the formula is
P = VI
What is the power consumption of a device operating at 12 V and drawing 2 A?
24 W
In the formula
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
, what does
E
E
E
represent?
Energy
A light bulb that transfers 600 joules of energy in 30 seconds has a
power
of 20 W
Match the variable with its symbol and units:
Power ↔️
P
P
P
, Watts
Energy ↔️
E
E
E
, Joules
Time ↔️
t
t
t
, Seconds
The formula to calculate power using voltage and current is
P = VI
What is the power consumption of a kettle operating at 230 V and drawing 10 A?
2300 W
Power can be calculated using either voltage and current or
energy
and time
What is the formula to calculate efficiency?
\text{Efficiency} = \frac{\text{Output Power}}{\text{Input Power}} \times 100%</latex>
An LED light bulb with 10 W input power and 8 W output power has an efficiency of
80%
1 watt is equivalent to 1 joule per
second
Which formula is used to calculate power using energy and time?
P
=
P =
P
=
E
t
\frac{E}{t}
t
E
What does the variable
x
x
x
represent in this study material?
Work done
The variable
t
t
t
represents time
Match the power unit with its symbol and definition:
Watt ↔️ W | Energy transfer of 1 joule per second
Joule per second ↔️ J/s | Equivalent to 1 watt
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