Charlene Kilgore PHY 102 April 11, 2014 Lillian Flakes Chapter 8 Review: Reading Check- 5 5. What kind of charge does an object acquire when electrons are stripped from it? A positive charge Think and Solve- Exercises- 71, 81,105 71. Why are objects with vast numbers of electrons normally not electrically charged? A charged object means an object deficient or with excessive electrons. There is no relation with quantity of electrons as it may contain the same number of protons to equal its charge. What’s important is the net charge 81. Why is a good conductor of electricity also a good conductor of heat? For both electricity and heat, the conduction is via electrons, which in a metal are loosely bound, easy mowing, and easy to start moving. 105. A car’s headlight dissipates 40 W on low beam and 50 W on high beam. Is there more or less resistance in the high-beam filament? Power is defined as P = V2 / R V –voltage R -resistance. When power increases then resistance decreases as the voltage applied is constant. Discussion Questions- 109, 110, 111, 119 109. In which of the circuits does a current exist to light the bulb? 110. Does more current “flow” out of a battery than into it? Does more current “flow” into a light bulb than out of it? Explain No, the current in a circuit is exactly the same in and out; because the same current goes in as what comes out; also because charges can never be created from nothing nor can it leave the circuit. 111. Sometimes you hear someone say that a particular appliance “uses up” electricity. What is it that the appliance actually consumes, and what becomes of it? An appliance doesn't "use up" electricity; it consumes energy; energy isn't used up either; it is simply converted from one form to another. In a lot of appliances, for example, electrical energy is converted into heat. 119. In the circuit shown, how does the brightness’s of the three identical light bulbs compare? Which light bulb draws the most current? What happens if bulb A is unscrewed? If bulb C is unscrewed? Bulb C is the brightest Bulb A draws the most current Bulb C & B would have the same brightness Bulb A&B would have the same brightness Chapter 9 Review: Reading Check- 7 7. Why is iron magnetic and wood not magnetic? It comes from the structure of an iron atom. The way the electrons group together makes one side of the atom have a high negative charge, and the other a high positive one therefore creating a force we call magnetic. Wood has no polarity so it is not magnetic. Think and Solve- Exercises- 52, 75, 87 52. What kind of force field surrounds a stationary electric charge? What additional field surrounds it when it moves? An electric field surrounds a stationary electric charge; a magnetic field surrounds it when it moves. 75. If your metal car moves over a wide, closed loop of wire embedded in a road surface, is Earth’s magnetic field within the loop altered? Does this produce a current pulse? Can you think of a practical application at a traffic intersection? In general yes. If there are any magnetic components in your car (the frame is usually made of iron alloys) then as they approach the loop, the field intensity penetrating the loop will vary and create a current pulse. This pulse can be used to trigger traffic signals to give you a green light at an intersection. 87. Can an efficient transformer step up energy? Defend your answer. No; energy is conserved and cannot be stepped up. When we increase the voltage, the current will decrease and therefore energy will remain conserved.