Energy & Power II
[////////// under construction
//////////]
Objectives
• Know that power is the rate of transfer of energy
• Know that power is measured in units of Watts, and
be able to explain what is meant by a power of 1 Watt
• Be able to solve numerical problems involving energy
and power.
Task 1  Recap
Remind the person next to you:
• The units used to measure efficiency
• What is meant by "an efficient device"
• What is meant by "an inefficient device"
Task 2
Power is the rate at which energy is transferred.
It is measured in units of Watts. A device with a power of 1 Watt
uses (or produces) 1 Joule of energy each second.
A 40 Watt light bulb uses 40 Joules of energy each
second.
It would use _______ Joules in 10 seconds.
It would use _______ Joules in one minute.
The formula connecting energy, power and time is very
simple:
P_{ }=
E ÷ t

P =
Power, measured in Watts (W)
E = Energy
transferred, measured
in Joules (J)
t = time taken,
measured in seconds (s) 
Make a note of the formula in your exercise book.
When you have finished, try to make an equation triangle from it  you
will need to think carefully about where each letter goes!
Task 3
Higher
Tier:
Try solving the
problems on
this sheet. Your
teacher will show you how to do the first two as an example.
Make sure you convert all quantities to standard units
before carrying out the calculation.
Foundation
Tier:
Try solving the
problems on
this sheet. Your teacher will show you how to do
the first two as an example. Pay attention for
any numbers that need changing into Watts or seconds.

Task 4
A
Homework/Extension
A
