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Rogue Physicist.  Free resources for physics education 2006-2016 Dorian Pascoe.  Email: dorian@top-school.co.uk

Most resources are available under a Creative Commons Licence.  Visit our mirror at www.physicsweb.altervista.org

 

 

Energy & Power II

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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