Lesson 12 — 2.5 Law of conservation of energy

• The law of conservation of energy
• Voortgezet speciaal onderwijs
• Leerroute 1

The law of

conservation of energy

The law of conservation of energy

• What is the law of conservation of energy?

• Can you think of real world examples?
  

• Where does energy come from?

• Where does energy go?
  

Checking the homework

This lesson

• Class discussion
  
• Checking the homework
• The law of conservation of energy
• Efficiency

Learning goals

• Describe the first two laws of thermodynamics in your own words.
• Give real world examples of the law of conservation of energy.
• Explain what is meant by useful energy and wasted energy.
• Explain what is meant by efficiency.

Watch the upcoming video.

Answer the following questions:

What are the first two laws of thermodynamics?

Why is it impossible to create a perpetual motion machine?

Exercise

What are the first two laws of thermodynamics?

• 1) Energy cannot be created or destroyed
  

• 2) Energy tends to spread out in the form of heath
  

Why is it impossible to create a perpetual motion machine?

• You cannot get more energy out then you put in.

• You loose energy in the form of heath.

Together with your neighbour 

think of three examples of the law of conservation of energy in real life

Exercise

Newtons Cradle

Link

The law of

conservation of energy

You cannot get more energy out than you put in

• Useful energy

• wasted energy

• Efficiency
  

80 J/s of electrical energy.

20 J/s of light energy

A construction lamp

60 J/s of thermal energy

The efficiency of a construction lamp

• A construction lamp uses 80 joules/second
  
• 20 J/s is turned into useful energy

• What is the efficiency of this construction lamp?
• It has an efficiency of 25%

Efficiency=(​totalenergy​​usefulenergy​​)⋅100

%

Efficiency=(​totalenergy​​usefulenergy​​)⋅100

%

=(​E​t​​​​E​u​​​​)⋅100

%

η

• η: efficiency (%)
  
• Eu: Energy useful (J)
  
• Et: energy total (J)
  

Working independently

Homework:

• The workbook exercises of 2.5 including E
  
• The yellow block exercises of 2.10
  

Learning goals

• Describe the first two laws of thermodynamics in your own words.
• Give real world examples of the law of conservation of energy.
• Explain what is meant by useful energy and wasted energy.
• Explain what is meant by efficiency.