LESSON 1

CURRICULUM  /  PHASE 4  /  ENERGY EFFICIENCY  /  LESSON 1
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Lesson Time: 45-75 minutes

LEARNING OBJECTIVES

STUDENTS WILL:

1

Explore what energy is

2

Understand the relationship between work and energy

3

Understand that energy is conserved

4

Practice calculating energy efficiency as the percentage of the total energy input that is output as desired work or energy

MATERIAL LIST

  • Journals or note-taking space for student reflection

  • Piper Computer Kit

  • Paper (scrap/used paper is preferred)

  • Scissors

  • Rulers

LESSON PREPARATION (10 MIN)
  • Read the resources yourself, and make sure you understand the energy calculations.

  • The suggested student to kit ratio is 2:1 up to 3:1. Students are in the same teams as before or make adjustments as necessary to facilitate good teamwork.

  • Make sure Piper kits are built, connected, functioning, and batteries are charged for the Raspberry Pi and the speaker.

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ENGAGE

Teacher-led Discussion (5-10 minutes):

What goes in and what comes out?

First, use slides #2 and 3 of the Energy Efficiency Lesson 1 Slide Deck to engage their prior knowledge of work, energy, and efficiency vocabulary.

 

After going through the slides, ask students the following questions:

  • Is all of the energy that goes in used to do useful work, or is some of it converted to other forms like heat, sound, or vibration?

    • Does all of the electricity that goes into a light bulb turn into light?

      • Example Answer: No. Some of it becomes heat.

 

How much goes in and how much comes out?

How efficient are light bulbs?:

Tell students: When a device consumes energy by transferring it to other types of energy, it is using power. The Piper Computer Kit’s screen is illuminated from the back using LEDs, a type of light bulb. Those LEDs use less than 2 Watts of power.

  • Provide the following information to them:

    • Show students this sample calculation for determining how much electricity an LED expends: 

      • A typical green LED like the ones in the Piper Kit uses 0.02 amps of electrical current at 2 volts. 
        To calculate: 0.02 A ✖️2.0 V = 0.04 Watts of electricity

      • Tell students: Most newer LEDs are over 95% efficient which means most of the energy consumed is actually utilized to light the screen!

 

New vs. Old

You can have students read this article about how much more power older computer’s use: https://www.extremetech.com/computing/97763-is-your-old-computer-costing-you-more-than-you-think

  • Ask students, are older computers more or less efficient than newer computers?

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EXPLORE

Explore: Big vs. Small

Ask students the following questions:

  • What uses more energy but does the same amount of work to carry the driver home, a motorcycle or a truck?

  • What takes more energy to keep cool or keep warm, a big building or a small building?

 

Show students slides #5 & 6 in the lesson slide deck before completing the activity below.
 

Have students explore a big screen vs. a small screen using the following instructions:

  • Cut out 9 pieces of paper the size of your Piper Kit’s screen.

  • Using a ruler, measure from one corner of the piece of paper to the opposite corner.

    • It should be approximately 9 inches (23 cm).

    • Television and computer screens are usually measured this way.

  • Using the cut out pieces of paper - how many pieces of paper does it take to make an 18-inch (46 cm) “screen”?

  • How many pieces does it take to make a 27-inch (69 cm) “screen”?

    • Is that a “big” screen?  How does it compare it to a TV screen you’ve seen before?

  • [Optional]: As a class, continue making bigger “screens” by combining each group's paper pieces.

  • What is the relationship? 

    • Each time the measurement doubles, how does the number of pieces of paper increase? (Possible Answer: It increases as the square: 22 = 4, 32 = 9, 42 = 16)

  • Let’s pretend that the Piper’s screen uses 1.5 Watts. Based on your measurement of the screen 

    • How many Watts would a 27-inch screen (monitor or TV) take to power?

      • Answer: 4.5 Watts

    • What about a 72-inch TV?

      • Answer: 12 Watts

    • NOTE: You can provide students with a hint if they are having trouble with the dimensional analysis:

      • If the Piper screen is 9 inches and utilizes 1.5 Watts of power then that means this type of screen utilizes ⅙ of a Watt per inch. To calculate the number of Watts, multiply the screen size in inches by ⅙.

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Explain (7-10 minutes):

Conduct a full class discussion using the following questions. Note: you can use a Think, Pair, Share to increase participation and confidence.

Discussion Questions: 

  • Which type of energy goes into the Piper Computer?  

  • Which type of energy comes out?

  • Is all of the electrical energy from the battery converted to light or sound?

  • After playing a bit of StoryMode on the Piper Computer, is the Raspberry Pi warmer? Why do you think this is the case? What is happening?

  • How can we measure and calculate energy use?

EXPLAIN
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ELABORATE

Apply: 

Show students slide #7 in the Energy Efficiency Lesson 1 Slide Deck.

 

Use the following activity to measure how much energy the Piper Computer uses:

  • Before you begin, make sure the battery for your Piper Kit is fully charged.

  • Note: This experiment may take some time, so it may be a good idea to start it at the beginning of a class period and check the battery throughout the lesson.

 

The battery’s capacity should be listed on the battery - look for a sticker or engraving that shows how many mAh (milliamp-hours) the battery is rated for. This is the battery’s capacity.  The example will use 7800 mAh. You’ll also need to find its voltage output. It should be 5VDC (volts direct current).

 

  • Start a timer or mark the time. If you don’t have a stopwatch or timer app on a phone, you can use this one: https://www.google.com/search?q=stopwatch

  • Every few minutes, check the battery’s gauge.  Stop the timer when it reaches 50%.

    • Note: If the Piper Kit's battery gauge has 4 levels, you could go to 75% (25% consumed), divide by 4 instead of two in the next step, etc....and it would only take half as long to run the experiment.

  • Calculate the power consumed by the Piper Kit:

    • Divide the battery’s capacity by 2, since we only used half of the battery.

      • 7800 mAh ➗2 = 3900 mAh

    • Convert this to Amp-hours by dividing it by 1000.  Just like there are 1000 mm in a meter, there are 1000 mAh in an Amp-hour (Ah).  

      • 3900 mAh ➗1000 = 3.9 Ah.

    • Next, we’ll find the power output by multiplying the capacity (3.9 Ah) by the voltage (5V):

      • 5 V ✖️3.9 Ah = 19.5 Wh (Watt-hours)

    • Finally, divide the battery’s power output by the hours it took to use half of the battery to calculate how many watts (on average) were used by the Piper Kit:

      • If it took 2 hours and 30 minutes: 19.5 Wh ➗2.5 h = 7.8 Watts

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Reflection (5 minutes):

[Optional]: You can show students the video on slide #8 to ensure they have bought into the purpose of these lessons and are ready for Energy Efficiency Lesson #2.

 

Have students reflect on what they learned using the Exit Ticket on slide #9.

 

EVALUATE