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Electricity and Magnetism Answers Worksheet 1 The man who lit up the world Time to Think (p. 9) 1. This invention makes it possible to change electrical energy to light energy in a practical way, thus producing a convenient, bright and safe light source from electricity. 2. Edison thought that a practical light bulb should have a wire of high resistance because a wire of high resistance will convert more electrical energy into heat. When the wire is very hot, it glows and emits light. 3. Edison filled the light bulb with nitrogen gas so that the light bulb had no oxygen inside to prevent the wire inside the bulb from burning. 4. This protects the interest of the inventor for a period of time during which only the inventor can make and sell the product of the invention. 5. (Open ended answer) This statement is true in some cases in which hard work is more important than bright ideas. Many of Edison’s inventions came from hard work. But in some cases the reverse is true, e.g. the finding of the structure of DNA by Watson and Crick. 6. He thought that Edison often worked by trial and error. If he could design his experiments based on some theory, he could have avoided doing many useless experiments. © Times Publishing (Hong Kong) Limited -1- Electricity and Magnetism Answers Worksheet 2 The man who captured lightning Time to Think (p. 15) 1. In both cases, there is an emission of light and heat through the air. 2. Franklin hypothesized that lightning occurred when electrical charges jumped from one cloud to the other. 3. In the kite experiment, he wanted to find out whether the clouds carried charges. His results showed that he succeeded in collecting the charges in the clouds with Leyden jars. 4. Based on his finding of lightning, he invented the lightning rod which protected tall buildings and structures from being struck and damaged by lightning. 5. When performing the kite experiment, one should avoid any direct contacts with the parts that carried the charges from the clouds, such as the wet string and the metal key to prevent from electric shocks. 6. Students may collect charges from different clouds with Leyden jars and show that some clouds have positive charges and some have negative charges. 7. The charges in the clouds are discharged to the lightning rod, which conducts the charges along a wire to the ground instead of through the building. -2- © Times Publishing (Hong Kong) Limited Electricity and Magnetism Answers Worksheet 3 The person who invented the first dynamo Time to Think (p. 21) 1. Faraday learnt science by reading the books he was given to bind, such as Encyclopedia Britannica and attending meetings of the City Philosophical Society and lectures of the Royal Institution to learn about the latest advances in science. 2. When Faraday heard that Ampère had used an electric current to turn iron inside a coil of wire into a magnet, Faraday thought that a magnet could cause an electric current to flow. 3. Faraday placed coils of wire near magnets in various ways to see whether an electric current could be generated in the wire. 4. When a current started to flow in the first coil, the magnetic field around the second coil suddenly increased as the iron ring became a magnet. 5. The transient current was generated by a change in magnetic force on the wire of the second coil. 6. When a steady current flowed in the first coil, there was no change in magnetic force on the wire of the second coil, hence no current is detected in the second coil. 7. When a bar magnet is moved in and out of a coil, there is a change in magnetic force on the wire of the coil, hence inducing a current to flow. © Times Publishing (Hong Kong) Limited -3- Electricity and Magnetism Answers 8. Students design their own dynamo. Example: a bicycle dynamo (Students should include materials, clear procedure and data and results obtained in operating the dynamo.) -4- © Times Publishing (Hong Kong) Limited