Physics 1 Revision
Lesson 3
Energy transfer and efficiency
Energy transfer
and efficiency
Energy cant be created or destroyed, it just turns into
another form
Energy transfer
diagrams show input, useful and
wasted energy
Wasted energy is usually heat & sound. This energy goes
into the surroundings
Chemical 
kinetic (useful)
sound (wasted)
heat (wasted)
An appliance that wastes les energy is called
energy efficient
Efficiency = useful energy / total energy
Energy efficient appliances can save you money
Energy is measured in Joules (J)
Filament light bulb
100 J
10 J
electrical
light
energy
energy
(input)
(output)
90 J
heat energy
(wasted)
Energy efficient light bulb
20 J
10 J
electrical
light
energy
energy
(input)
(output)
10 J
heat energy
(wasted)
Sankey
diagrams
are a way to show energy
efficiency
The thicker the arrow ,
the more energy input/
output
How long it takes to recover the costs of an appliance
is called
pay back time
If loft insulation costs £200 to install and saves you
£50 a year in heating bills… the pay back time is 4
years
Ways to make a home
energy efficient
Energy saving light bulbs
Cavity wall insulation
Loft insulation
Draft excluders
Double glazing
The double-glazing for a
house costs £3,000 but
saves £150 per year in
fuel costs. What is its
payback time?
The cavity wall insulation in a house
costs £6000 to install. It has a
payback time of 15 years. How much
money does the insulation save each
year in fuel costs?
Transferring
electrical energy
Electrical energy is measured in kW/h
Electrical energy = power (kW) x time (h)
The longer you use an appliance for the more
electrical energy it will
transfer
Electricity costs money
The electricity company charges you for every
you use
unit
1 unit = 1 kW/h
cost =
number of units
x cost per unit
Example:
How much would 10 units of
electricity cost at a price
of 9p per unit?
Key words and
statements
Energy transfer and efficiency
Input energy
How well a device transforms input energy into
useful energy
Useful energy
The unit for energy
Wasted energy
The amount of energy in joules that is
transferred into the wrong type of energy
Energy efficiency
The amount of electrical energy used and can be
measured by power (kW) x time (h)
Joules
The unit is kW/h.
The amount of energy in joules that is
transferred into the right type of energy
Pay back time
Is equal to 1kW/h
Electrical companies charge consumers by units
Electrical energy transfer
Number of joules that enters the device
Unit of electricity
The time it takes to recover the cost of an energy
efficient appliance before you can start saving
money
Energy transfer and efficiency
Input energy
How well a device transforms input energy into
useful energy
Useful energy
The unit for energy
Wasted energy
The amount of energy in joules that is
transferred into the wrong type of energy
Energy efficiency
Is measured in kW/h
The amount of electrical energy used and can be
measured by power (kW) x time (h)
Joules
The amount of energy in joules that is
transferred into the right type of energy
Pay back time
Is equal to 1kW/h
Electrical companies charge consumers by units
Electrical energy transfer
Number of joules that enters the device
Unit of electricity
The time it takes to recover the cost of an energy
efficient appliance before you can start saving
money
Energy transfer and efficiency
Energy cannot be…
Turns more of it’s input energy into useful energy
and wastes less energy
Wasted energy is usually…
But will save money in the long term. The time is
takes to recover the cost of the device is called
pay back time
An energy efficient device…
Heat or sound and goes into the surroundings
A Sankey diagram…
The more electrical energy it will transfer
Energy efficient devices usually coast money to
install…
You use the appliance for longer and when the
appliance uses a greater amount of power
The longer an appliance is used for…
Created or destroyed
The cost of using an appliance will increase when…
It will take 8 years to pay back the cost
If solar panels cosy £2000 pounds to install and it
saves £250 pounds in electricity bills per year…
Is a graph showing input, useful and wasted joules
Energy transfer and efficiency
Energy cannot be…
Turns more of it’s input energy into useful energy
and wastes less energy
Wasted energy is usually…
But will save money in the long term. The time is
takes to recover the cost of the device is called
pay back time
An energy efficient device…
Heat or sound and goes into the surroundings
A Sankey diagram…
The more electrical energy it will transfer
Energy efficient devices usually cost money to
install…
You use the appliance for longer and when the
appliance uses a greater amount of power
The longer an appliance is used for…
Created or destroyed
The cost of using an appliance will increase when…
It will take 8 years to pay back the cost
If solar panels cosy £2000 pounds to install and it
saves £250 pounds in electricity bills per year…
Is a graph showing input, useful and wasted joules