lesson 11 — 2.10

Energy
Calculations + §2.6 & 2.7
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Slide 1: Slide
energy calculationsMiddelbare schoolhavo, vwoLeerjaar 1

This lesson contains 20 slides, with text slides and 1 video.

Items in this lesson

Energy
Calculations + §2.6 & 2.7

Slide 1 - Slide

Slide 2 - Video

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


Slide 3 - Slide

Recap

Slide 4 - Slide


  • Useful energy

  • wasted energy

  • Efficiency

Slide 5 - Slide

Efficiency=(totalenergyusefulenergy)100
%

Slide 6 - Slide

Efficiency=(totalenergyusefulenergy)100
%
=(EtEu)100
%
η
  • η: efficiency (%)
  • Eu: Energy useful (J)
  • Et: energy total (J)

Slide 7 - Slide


2.10 

Energy snaky diagram

Slide 8 - Slide

Which lamp is more efficient?
A
B

Slide 9 - Slide

Slide 10 - Slide

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.

Slide 11 - Slide

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


Slide 12 - Slide

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


=(EtEu)100
η
%

Slide 13 - Slide

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


=(EtEu)100
η
%
=(85706070)100
η
% = 70,8 % 

Slide 14 - Slide

Calculations — Exercise 2
A machine has an efficiency of 25 %. It creates 350 joules of useful work. Calculate its total energy input.

Slide 15 - Slide

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

  •  η = 25 %
  • Euseful = 350 J

Asked
  • Calculate the total energy input of this machine

Fromula


Calculation


Slide 16 - Slide

Given

  •  η = 25 %
  • Euseful = 350 J

Asked
  • Calculate the total energy input of this machine

Fromula


Calculation


Slide 17 - Slide

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?

Slide 18 - Slide

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
  • EWasted = 32450544 J
  • Etotal = 8.9 x 3153600 x 1.5 = 42100560 J
  • Euseful = 42100560  - 32450544 = 
      9650016 J

Slide 19 - Slide

Given
  • 8.9 liters per 100 kilometer
  • one liter contains 3153600 joules
  •  a car drives 150 kilometrer
  • EWasted = 32450544 J
  • Etotal = 8.9 x 3153600 x 1.5 = 42100560 J
  • Euseful = 42100560  - 32450544 = 
      9650016 J

Slide 20 - Slide