This activity is a great way to start Chapter 2. Students will be amazed that they can use such simple equipment to “listen in” on the coded signals produced by remote controls. Although the word infrared is never introduced in the activity, that’s exactly the type of signal that is sent from an infrared remote control to a TV, VCR, or DVD player. The only specialized piece of equipment required is the photovoltaic cell described in the introduction to Lesson 2.1. Science 30 © 2007 Alber ta Education (www .education.go v.ab .ca). Third-par ty cop
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In terms of organization, Part A of this activity is best done in the classroom since photovoltaic cells are required. Students can be asked to bring in the headphones they use with their portable music players. Old remote controls that have been “orphaned” by broken machines can be donated from parents, teachers, and students within your school community in the weeks prior to the lab activity.
Part B of this investigation is best done as a homework assignment, assuming that each student has access at home to a device that is operated by remote control. An alternative is to do this activity as a demonstration using a pair of volunteers to operate the remote control while the rest of the class observes and records the results.
Part a: Listening to the Coded Signal Procedure and Observations
The differences in the sounds resulting from pressing different keys on the same remote control can be quite subtle. The differences heard between different models and makes of remote controls can be dramatic. A common feature of all of these signals is a pulsed clicking or beeping sound.
Part B: Properties of the Waves Emitted by Remote Controls Procedure and Observations
The results for Part B can vary due to a number of things, such as freshness of the batteries in the remote control, distance from the machine, and sensitivity of the machine to changes in signal strength.
Shielding
Material Observed Effect on the ability of theRemote Control to Send a Signal
one sheet of paper The remote control was still able to send a signal to the TV.
metal cookie sheet The remote control was not able to send a signal to the TV.
transparent glass full of water The remote control was still able to send a signal to the TV.
glass of milk The remote control was not able to send a signal to the TV.
sheets of tissue The remote control was able to send a signal to the TV through seven sheets of tissue but not eight.
analysis
1. Differences were heard between the sounds produced by different brands of remote controls. This suggests that different brands of remote controls send different types of signals. Since each television must be able to respond to its own brand of remote control, it makes sense that a different brand of remote control would not be able to produce the unique signal for that television.
2. chemical energy in batteries electrical energy in circuits of remote control electrical energy in photovoltaic cell energy in signal sent by remote control electrical energy in headphones mechanical energy in headphones sound energy from headphones Science 30 © 2007 Alber ta Education (www .education.go v.ab .ca). Third-par ty cop
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As described in the introduction to the chapter, this lesson provides students with an introduction to the nature of electromagnetic radiation and then provides an opportunity for them to survey the major regions of the electromagnetic spectrum. Other than the use of the universal wave equation, the approach is qualitative, with a focus on applications and some unique hands-on activities.
The Use of Photovoltaic Cells
Three of the four student activities in this lesson, as well as the “Exploring Coded Signals” activity from the chapter introduction, utilize photovoltaic cells. This enables students to explore the properties of infrared radiation. These activities are not that complicated, are quite effective at demonstrating concepts, and are very motivating for students—in short, ideal for Science 30 students.
The photovoltaic cells recommended for these activities come complete with leads or contacts to allow easy connection to an external circuit and are capable of producing an output of at least 0.2 A at 0.4 V. These cells may not be easy to find at local electronics stores. Ordering from scientific supply companies or from online vendors may be your only option.
Among the many possible online vendors, two are listed here:
• Ward’s Natural Science sells a “solar cell” that would work nicely. At the time of publication, this cell was described on the Ward’s website:
http://wardsci.com/product.asp_Q_pn_E_Ig0003272_a_Solar+Cell
• Silicon Solar sells an educational solar kit, called “DemoKit.” It includes a large solar cell, a small motor, and a few other attachments. At the time of publication, this kit was described on Silicon Solar’s website:
http://www.siliconsolar.com/shop/catalog/DEMOKIT-Solar-Kit-p-118.html
The use of photovoltaic cells in this chapter lays a solid foundation for the work students will do with alternative methods of generating electrical energy in Unit D.
Teaching Strategies
Practice, page 413
1. The word radiation is similar to the word radius. This makes sense because the types of radiation in the photograph travel out from the Sun along paths that could each be described as a radius drawn from the centre of the Sun.
2. a. No, cosmic rays cannot be classified as a form of electromagnetic radiation because electromagnetic radiation consists only of electric and magnetic fields travelling at right angles to each other. Cosmic rays consist of a stream of positively charged particles.
Lesson 2.1: Electromagnetic Radiation
Science 30 © 2007 Alber ta Education (www .education.go v.ab .ca). Third-par ty cop
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b. Light is a type of electromagnetic radiation that can be detected by human eyes. People see starlight because it travels from the stars to Earth. In other words, every time you see a star, you are looking at electromagnetic radiation from that star.
Practice, page 414
3. You could detect the radiant heat with the heat-sensitive nerve cells in your fingertips or your face. You could detect the visible light emitted by the light bulb with the light-sensitive nerve cells on the retina at the back of your eye.
4. Unlike sound waves or water waves, light does not need matter to vibrate and transmit energy. The energy in a light wave is transmitted through the vibrations of electric and magnetic fields. Since electric and magnetic fields are not a form of matter and are able to exist in a vacuum, light energy is able to pass through the near vacuum from the hot filament to the glass of the bulb.