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Answer Key__ Name: __ Pretest score: _____/52 Posttest score: _ 52_/52 Ch 16: Electricity Pretest N__ unit used to measure resistance 1. __ A. alternating current B. Ampere G__ when electrons flow in 1 direction 2. __ C. circuit breaker D. conductor Q__ drawing of an electric circuit 3. __ E. Coulomb F. current W__ potential difference as a charge moves 4. __ through an electric field G. direct current H. electrical charge L__ a piece of wire in a circuit set to melt and I. electrical field break the circuit if it overloads J. electric force 5. __ F__ flow of electrons through a conductor 6. __ K. electrical potential energy L. fuse U__ material that has no resistance at very 7. __ low temperatures H__ positive (+) and negative (-), like ones repel 8. __ and opposite ones attract M__ substances that stop electrons from flowing 9. __ M. insulator N. Ohm O. parallel circuit P. resistance/resistors Q. schematic R. semiconductors A__ electrons move back and forth in a 10. __ conductor due to changing electric fields I 12. __K__ ability to move charges from one area to 11. __ __ a region of space with an electric charge another E__ unit of electric charge S. series circuit T. short circuit U. superconductor V. Volt W. voltage 13. __ S__ when electricity has only 1 path to follow, no matter how many things 14. __ (e.g. lights) are on it P__ objects that are connected to an electric current and act to slow the flow 15. __ of electricity D__ substances that allow currents to flow 16. __ V__ unit of electric potential 17. __ R__ a material that is neither a very good conductor or insulator 18. __ J__ attraction or repulsion between two objects 19. __ T__ an alternate pathway for current from the circuit, often undesirable 20. __ O__ two or more paths for a current to follow 21. __ B__ unit that measures current 22. __ C__ a magnet or strip of 2 metals that opens a circuit when it overloads 23. __ 24. - 25. What will these two charges do? Explain why. They will be attracted and move towards each other because they are opposite charges 26. – 27. The strength of an electric field depends on two things. Name them and explain whether it is a direct or indirect relationship. Amount/strength of charge…direct (more charge = more force) Distance between charges…indirect (more distance = less charge) 28. – 30. There are three ways something can become charged. Name/explain them. Friction…rubbing things together Induction…one charged thing close to an uncharged one Contact…one charged thing touching an uncharged one 31. – 32. Explain the difference between direct and alternating current and a source of each. Direct current is when charges move in one direction around a circuit. Batteries provide direct current Alternating current is when the charges move back and forth. Your house is alternating current. 33. Describe the relationship between resistance, voltage and current. R = V/I (really I = V/R, flow = push/slowing) a. resistance stays the same: current increases if voltage increases. (slowing stays same, flow goes up if push goes up) b. current stays the same, increased resistance needs increased voltage. (flow is the same, so if slowing goes up, you need more push) c. voltage remains the same, increased resistance means decreased current. (push remains the same, so if slowing goes up, flow will go down) 34. – 36. Electric flow is often compared to flow of water. Explain how each picture shows this for voltage, amperage and resistance. Voltage = potential; it’s the “push” making electrons want to move (like water in a tower vs. on the ground) Current = flow; it’s how fast the electrons flow (like flow through a big tube vs little tube) Resistance = slowing flow; it’s what’s slowing the electrons down (like squeezing through a narrow tube) 37. – 42. Identify each of these electric symbols: wire_ __ battery_ __ __ __ open switch_ __ 43. Use the symbols bulb, 1 battery and 1 switch. resistor_ light bulb_ closed switch_ __ to draw a simple circuit with 1 light 44. Use the symbols to draw a circuit with 1 battery and two light bulbs connected in series. 45. For the same circuit as #44, if I add another light bulb what will happen to the brightness? Explain. It will decrease (become dimmer)…the voltage is spread over 3 resistors (push is the same, so more slowing means less flow) 46. For the same circuit as #44, if I add another battery what will happen to the brightness? Explain. It will increase (become brighter)…there is in creased voltage (more push with the same slowing means more flow with the same slowing) 47. Use the symbols to draw a circuit with 1 battery and two light bulbs connected in parallel. 48. For the same circuit as #47, if I add another light bulb what will happen to the brightness? Explain. Nothing! Each individual circuit has the same voltage (brightness) because each individual circuit has 1 lightbulb. (each “circle” is its own circuit, so adding a third “circle” still has the same amount of push, flow and slowing in each circle.) 49. For the same circuit as #47, if I add another battery what will happen to the brightness? Explain. Both will increase (become brighter)…there is increased voltage across each individual circuit (each “circle” is its own circuit, so adding more push and keeping slowing the same means more flow.) Will the following circuits work (light the bulb)? Explain why. 50. No…the circuit is not complete. 51. Yes…you have a complete circuit, a power sources (2 batteries) and a resistor (light bulb) 52. A B Light A no…the switch is open Light B…yes, you have a complete circuit, a power source (battery) and a resistor (light bulb)