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G9 G) Energy, Work and Power - Efficiency

This document defines efficiency and discusses how to calculate it using the efficiency formula. It provides examples of calculating efficiency from word problems involving energy transfers. Sankey diagrams are introduced as a way to show energy inputs and outputs. Worked examples demonstrate calculating the efficiency of processes where useful work is done by lifting a weight and producing light from electrical energy. Learners are directed to an online worksheet to practice these calculations.

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Alhasan Almoaqaleh
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© © All Rights Reserved
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46 views

G9 G) Energy, Work and Power - Efficiency

This document defines efficiency and discusses how to calculate it using the efficiency formula. It provides examples of calculating efficiency from word problems involving energy transfers. Sankey diagrams are introduced as a way to show energy inputs and outputs. Worked examples demonstrate calculating the efficiency of processes where useful work is done by lifting a weight and producing light from electrical energy. Learners are directed to an online worksheet to practice these calculations.

Uploaded by

Alhasan Almoaqaleh
Copyright
© © All Rights Reserved
Available Formats
Download as PDF, TXT or read online on Scribd
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g) Energy, work and power:

Efficiency
You will be able to:

● Define Efficiency and find the efficiency of energy transfers.


● Define sankey diagrams.
● State the efficiency formula as (useful energy output/
energy input) ×100%.
● Solve word problems involving energy efficiency.
Starter activity

Efficiency
Describe the energy transfer
in water kettle.

Electrical energy 🡪 internal energy

What does it mean when a machine is


described as “efficient”?
The machine transfers energy
at a great rate without large loss
of energy.
Heat the water faster & quick

The machine transfers energy at a


great rate with least energy loss
Refresher activity

Energy Sankey Diagrams


Sankey diagrams are diagrams to show how the energy
input into something is used. For example, if 100J (100 Joules) of
electrical energy is input, and 90J is (wasted) heat energy and the
other 10J is light useful energy, we could demonstrate it on a
Sankey diagram, like this:
The width of the arrows symbolise
how many joules are being used as
that type of energy - say if on our
diagram 1cm = 10J, we would make
the arrow for heat energy 9cm long
to show that the amount of electrical
energy being transferred into heat
energy is 90j.
Efficiency formula
Efficiency can be calculated using the formula:
useful energy output / total energy input.
It can be measured in either percentage or decimal format.

Efficiency =
(useful energy output/ energy input)
Percentage Efficiency =
(useful energy output/ energy input) ×100 %
Efficiency does not have units or %
What does it mean when a machine is described as
Efficient:
Efficient: achieving maximum productivity with
minimum wasted effort or expense.
In real life
In a system, some of the energy is lost as waste.
i.e heat energy resulting of friction
Worked example 1:
An electric motor raises a weight of 150 N through a height
of 7.2 m. The energy supplied to the motor during this process
is 3.5 × 104 J.
Calculate:
a) the increase in gravitational potential energy
b) the efficiency of the process.

Solution:
a) EP = 150 × 7.2 = 1080 J
b) Efficiency = useful work out /energy in =
= 1080/ 3500 = 0.31 or 31%
Worked example 2:
A filament bulb is supplied with 100 J of electrical
energy. 45 J is converted to light energy.

Efficiency % = 45 /100 =
= 0.45 = 45 %

Is this bulb efficient?


Color Gauge in plenary
Activity1:
To start the Assigned worksheet in google classrooms, go to Classwork
Tab/ Q2 Classwork/ Solve Question in
Efficiency calculations Worksheet,
after you finish, please revise & Submit, then Mark as done.

Go to GC to solve
worksheet

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