A Circuit Design Challenge

Transcription

1 24 LESSON A Circuit Design Challenge INTRODUCTION Throughout this module, you have investigated and observed energy transfer in electrical systems. In this lesson, you will be able to apply what you know about electrical systems in a technological design challenge. Your group will role play an engineering team whose task is to design and build an electrical circuit that controls a device or system as specified in a design brief. Your team will then demonstrate the control system to the class and explain the scientific and design principles you used to create it. COURTESY OF THE CHICAGO TRIBUNE A fast-food robot. Want fries with that? OBJECTIVES FOR THIS LESSON Design and build an electrical circuit that controls a device. Demonstrate your control system to the class. Explain the scientific principles you used to design your control system. 244 STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N

2 Getting Started Read and discuss with your group the design briefs on Inquiry Master 24a: Design Challenges. Choose a design challenge for your group to complete. Answer the following questions on Student Sheet 24.1: Engineering Team Report: A. What design challenge did your group choose? B. What criteria will you use to assess how successful your design is? MATERIALS FOR LESSON 24 For you 1 copy of Student Sheet 24.1: Engineering Team Report For your group 1 copy of Inquiry Master 24a: Design Challenges 1 circuit systems kit Additional electrical components and materials provided by your teacher C. What are the constraints of the design challenge you chose? STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N 245

3 LESSON 24 A CIR CU IT DES IGN CHAL LENGE Inquiry 24.1 Designing and Building Your Own System PROCEDURE Work as an engineering team to design an electrical system that will control the device or devices as specified in the design brief for the challenge your group chose. Design your system using the components in your circuit systems kit plus any other components provided by your teacher. Draw a schematic of the circuit you designed for your control system on the student sheet. You may also wish to draw a picture of what your completed system will look like. Build and test your system to see that it performs as described in the design brief. If it does not, redesign or modify your circuit until it does. Use your student sheet to keep track of what you have learned and the modifications you made to your design Complete questions 5 8 on the student sheet to evaluate your final design and outline changes you would make if you could. Demonstrate your group s control system to the class. In your presentation, describe the scientific and design principles you used to create your control system. REFLECTING ON WHAT YOU VE DONE You have just completed a process called technological design. Review with the class the process you followed in completing your technological design challenge. Discuss with the class how the technological design process is different from the scientific inquiry activities you have completed in this module. Write a response to the following statement in your science notebook: Technological design and scientific inquiry are different, but they depend on each other. 246 STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N

4 LESSON 24 A CIRC UIT DES IGN CHAL LE NGE Generating Electrical Power In 1997, the world used 12 trillion kilowatt-hours of electrical energy. That s 12,000,000,000,000 kilowatt-hours or 12 million-million kilowatthours! If that seems like a lot, then consider this: By 2020, the world is expected to almost double its electrical energy needs to 22 trillion kilowatt-hours each year. Where is all this electrical energy used? And how is it produced? (continued) CORBIS/ROYALTY-FREE As cities grow, electrical energy needs grow with them. STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N 247

5 LESSON 24 A CIR CU IT DES IGN CHAL LENGE Worldwide Use of Electricity Those 12 trillion kilowatt-hours are used all over the world. Some places use more than others. In 1997, the United States used about one-quarter of all the electrical energy that was produced. That s about 3.3 trillion kilowatthours. In comparison, China used only about 4 percent of the electrical energy generated worldwide. And China has more than four times as many people as the United States! During the first two decades of the 21st century, the amounts of energy used are expected to change. While electrical energy demand is expected to increase worldwide, it is predicted to increase faster in some countries than in others. Demand for electricity is expected to increase slowly in the United States. In 2020, the United States will use 4.3 trillion kilowatthours of electrical energy. That s an increase of 1 trillion kilowatt-hours over 23 years. While that may seem like a large increase, look at some of these other changes. In places like China, South America, and Central America, the electrical energy demands are expected to increase dramatically. As these places begin making more products, they are expected to use more electrical energy. These areas will also expand the availability of electrical energy. In 1997, only about one-third of the people in Central America had access to electric utilities. But by 2020, people in South and Central America are expected to need 1.6 trillion kilowatt-hours of electrical energy each year. That s more than three times as much as in Similarly, China is expected to need 3.5 trillion kilowatt-hours of electrical energy by Compare that to the 0.5 trillion used in Electrical Energy in the United States How electricity is generated varies widely from region to region in the United States. In the Northwest, a lot of electrical energy is generated with hydropower, while in West Virginia most of the electrical energy is generated with coal; Alaska relies heavily on natural gas. But how do Americans use energy? It s easy to see how electrical energy is used in houses for appliances like refrigerators, toasters, and many water heaters, but only about one-third of all electrical energy produced in the country is used in homes. About another one-third is used for commercial purposes in office buildings, schools, and stores. And a little less than one-third is used in industry, where it helps make many of the products for sale in stores. Finally, 1 percent of the electrical energy produced in the United States is used in transportation. In individual homes, on average, nearly onethird of energy consumption is used for heating and cooling the house and heating water. Two other major consumers of electrical energy are refrigerators and lighting, which each use about 10 percent of the electricity used in a home. Other uses such as computers, televisions, and dishwashers represent only 1 3 percent of an average household s electricity usage. It will require a major effort to keep meeting the increasing demands for electrical energy around the world. Scientists and engineers are working hard to design more efficient electrical systems to slow down the increasing demand, but new and better ways are also being explored to generate more electrical energy. QUESTIONS 1. In what parts of the world is electrical energy most likely to increase the fastest? 2. What appliances in the house use the most electrical energy? 3. Make a pie chart showing electrical energy usage in the United States. 248 STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N

6 LESSON 24 A CIRC UIT DES IGN CHAL LE NGE Creating Creating Television Have you ever thought about television while doing your chores? In 1920, a 14-year-old boy name Philo Farnsworth did. But, probably unlike you, Philo wasn t thinking about his favorite program. Why? Because televisions didn t exist then. When Farnsworth thought about television, he was imagining how to make one that worked. Making an Idea a Reality Farnsworth had to learn a lot before he could transform his ideas into a working television. He studied science, especially electricity. He even stayed after school with his teacher to (continued) BETTMAN/CORBIS Philo Farnsworth made significant contributions to the development of television. He is seen here with an early model television. STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N 249

7 LESSON 24 A CIR CU IT DES IGN CHAL LENGE BETTMAN/CORBIS The interior of Farnsworth s early television. The image of Joan Crawford, a popular movie star at the time, appears on the screen of the cathode-ray tube, an essential component in the television. 250 STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N

8 LESSON 24 A CIRC UIT DES IGN CHAL LE NGE learn more. While in high school, he made a sketch of an electronic tube for his television. After only 2 years of high school, Farnsworth went on to college to continue his studies. Philo had to leave college before he graduated, but that didn t keep stop him from working on his project. He took his idea to investors and convinced them to fund his work. With the money, he set up a lab and went to work making a television system. In 1927, he made a working set and applied for a patent. This led to a legal battle with Vladimir Zworykin, another inventor. Zworykin had already applied for a patent for an electronic television. But Zworykin didn t have a working model. After years of legal battles, Farnsworth finally won. The Image Dissector As the patent battle shows, Farnsworth was not the first person to try to invent television. Inventors had been trying to make an electronic television for more than 30 years. They knew that two things were needed to send a moving picture from one place to another a transmitter and receiver. The transmitter would have to detect an image as separate points of light. These points of light then had to be converted into electrical impulses. The impulses had to be transmitted to a receiver. The receiver collected the impulses and converted them back into points of light. The points of light recreated the original image. When the system was built, the receiver was the first electronic television. Several inventors had built a mechanical television that relied on a spinning disc to break up the image. Farnsworth had a different idea. He used a beam of electrons to scan an image and turn it into electrical impulses. These impulses could be transmitted to a receiver. Farnsworth named the device that did this an image dissector. He also created a receiver that contained a picture tube (cathode-ray tube). The picture tube used a stream of electrons and a screen to recreate the original image. He used his image dissector and picture tube to start transmitting images in Television Evolves Farnsworth s first television would barely be recognizable by today s standards. His system produced a black-and-white image just over 2.5 cm tall. But it was an important breakthrough in technology. In the next 10 years, he and other inventors made many improvements. Farnsworth increased the number of lines in the image. Zworykin created better camera tubes. And an inventor named Allen DuMont made improvements to the cathode-ray tube. Color television appeared in the 1950s. So did the first remote controls. Continued improvement of cathode-ray tubes made televisions smaller. More recent television advances include plasma screens, digital TV, and high-definition TV. The history of television is not simply the story of one person. It shows how a great idea inspired a whole group of inventors and scientists. Advances in television design continue today. Televisions are getting slimmer (and smaller) due to improvements in electronics and computer technology. SONY PLASMA WEGA KZ-42TS1 PLASMA TV STC/MS E L E C T R I C A L E N E R G Y A N D C I R C U I T D E S I G N 251