lesson 11 — 2.10

• energy calculations
• Middelbare school
• havo, vwo
• Leerjaar 1

Energy

Calculations + §2.6 & 2.7

In pairs of two

Step 1) 

For 10 minutes

• One of you reads and takes notes of §2.6.
  
• The other reads and takes notes of §2.7
  

Step 2)

Discuss what you learned

• Go over each others notes
• think of one question per paragraph
  

Step 3

• Share your notes with another pair close to you
  

Recap

• Useful energy

• wasted energy

• Efficiency
  

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

%

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

%

=(​E​t​​​​E​u​​​​)⋅100

%

η

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

2.10 

Energy snaky diagram

Which lamp is more efficient?

A

B

Calculations — Exercise 1

Consider a machine that puts out 6070 joules of useful work. As a by product it also produces 2500Joules of heat.

Calculate the efficiency of this machine.

Consider a machine that puts out 6070 joules of useful work. As a by product it also produces 2500Joules of heat.

Calculate the efficiency of this machine.

Given

• Eu = 6070 J
  
• Ew = 2500 J
  
• Et = 6700 + 2500 = 8570 J
  

Asked

• Calculate the efficiency of this machine
  

Fromula

Calculation

Consider a machine that puts out 6070 joules of useful work. As a by product it also produces 2500Joules of heat.

Calculate the efficiency of this machine.

Given

• Eu = 6070 J
  
• Ew = 2500 J
  
• Et = 6700 + 2500 = 8570 J
  

Asked

• Calculate the efficiency of this machine
  

Fromula

Calculation

=(​E​t​​​​E​u​​​​)⋅100

η

%

Consider a machine that puts out 6070 joules of useful work. As a by product it also produces 2500Joules of heat.

Calculate the efficiency of this machine.

Given

• Eu = 6070 J
  
• Ew = 2500 J
  
• Et = 6700 + 2500 = 8570 J
  

Asked

• Calculate the efficiency of this machine
  

Fromula

Calculation

=(​E​t​​​​E​u​​​​)⋅100

η

%

=(​8570​​6070​​)⋅100

η

% = 70,8 % 

Calculations — Exercise 2

A machine has an efficiency of 25 %. It creates 350 joules of useful work. Calculate its total energy input.

A machine has an efficiency of 25 %. It creates 350 joules of useful work. Calculate its total energy input.

Given

•  η = 25 %
• E_useful = 350 J

Asked

• Calculate the total energy input of this machine
  

Fromula

Calculation

Given

•  η = 25 %
• E_useful = 350 J

Asked

• Calculate the total energy input of this machine
  

Fromula

Calculation

Calculations — Exercise 3

An average car uses 8.9 liters of gasoline per 100 kilometre. One liter of gasoline contains 31536000 joules. If a car drives 150 kilometre, and during this journey it creates 32450544 joules of heat and sound energy combined, what would be its efficiency?

An average car uses 8.9 liters of gasoline per 100 kilometre. One liter of gasoline contains 31536000 joules. If a car drives 150 kilometre, and during this journey it creates 32450544 joules off heat and sound energy combined, what would be its efficiency?

Given

• 8.9 liters per 100 kilometer
• one liter contains 3153600 joules
•  a car drives 150 kilometrer
• E_Wasted = 32450544 J
• E_total = 8.9 x 3153600 x 1.5 = 42100560 J
• E_useful = 42100560  - 32450544 = 

      9650016 J

Given

• 8.9 liters per 100 kilometer
• one liter contains 3153600 joules
•  a car drives 150 kilometrer
• E_Wasted = 32450544 J
• E_total = 8.9 x 3153600 x 1.5 = 42100560 J
• E_useful = 42100560  - 32450544 = 

      9650016 J