lesson 10 — 1st online lesson

• energy calculations
• Voortgezet speciaal onderwijs
• Leerroute 1

2.10 Energy 

calculation's

Learning goals

• Give examples of useful energy and wasted energy
  

• Explain what is meant by efficiency
  

• Be able to do calculations that involve energy
  

• Useful energy

• wasted energy

• Efficiency
  

Useful energy

• The amount of joules that do the work you want
  

Wasted energy

• The amount of joules that do work that you don't want
  

Efficiency

• The percentage of the total energy input that gets converted into useful energy.
  

The efficiency of a construction lamp

• A construction lamp uses 80 joules/second
  

• It produces 20 J of light energy per second.

• It produces 60 J of thermal and sound energy per second.
  

The efficiency of a construction lamp

The efficiency of a construction lamp

Useful

The efficiency of a construction lamp

Useful

Wasted

The efficiency of a construction lamp

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

%

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

%

=(​E​t​​​​E​u​​​​)⋅100

%

η

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

The efficiency of a construction lamp

Calculate the efficiency of the lamp of this energy transformation diagram 

Given:

• Total energy = 80 Joule
  
• Useful energy = 20 J
  

Asked:

• Calculate the efficiency of this lamp
  

Formula:

Calculation:

Calculate the efficiency of the lamp of this energy transformation diagram 

Given:

• Total energy = 80 Joule
  
• Useful energy = 20 J
  

Asked:

• Calculate the efficiency of this lamp
  

Formula:

Calculation:

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

%

Calculate the efficiency of the lamp of this energy transformation diagram 

Given:

• Total energy = 80 Joule
  
• Useful energy = 20 J
  

Asked:

• Calculate the efficiency of this lamp
  

Formula:

Calculation:

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

%

Efficiency=(​80​​20​​)⋅100

%

=25

%

A certain light bulb uses 200 J of electrical energy. 

It produces 20 J of light energy. 

Calculate its efficiency

1. 10 %
2. 5%
3. 20%
4. 40%

These fairy lights use 230 J of electrical energy and produce 92 J of light energy. Calculate their efficiency

1. 20 %
2. 25%
3. 40
4. 60%

Total energy = 1000000J

Useful energy = 650000J

Calculate the efficiency of this airplane.

1. 50%
2. 65%
3. 35%
4. 80%

Learning goals

• Give examples of useful energy and wasted energy 
  

• Explain what is meant by efficiency
  

• Be able to do calculations that involve energy