and the charge on a proton is +e. We never see objects that have a charge which is not a whole number multiple of this number.

Transcription

1 Name: Physics Chapter 17 Study Guide Useful Information: e = 1.6"10 #19 C k = 9 "10 9 Nm 2 C 2 $ 0 = 8.85 "10 #12 C 2 N "m 2 PE electric = q%v %V = #Ed %V = kq C = Q C = $ 0A PE r V d capacitor = 1 %Q 2 QV I = R = %V %t I P = IV A Basic Understanding: Chapter 17 Odd Numbered Core Problems Chapter 17 Review Problems:! 5, 8, 9, 18, 20, 27, 28, 29, 33, 41, 47, 55, 57, 59, 75, 77. Pushing to be Better: Chapter 17 Your Try Problems Chapter 17 Even Numbered Core Problems Chapter 17 Review Problems: 3, 4, 10, 12, 13, 17, 19, 23, 25, 26, 30, 31, 32, 34, 35, 39, 40, 42, 43, 44, 45, , 54, 56, 60, 61, 64, 65, 67, 69, 74, 79. Standardized Test Prep Digging Deeper: Chapter 17 Review Problems: 2, 6, 15, 16, 21, 52, 63, 73, 80. Individual Inquiry Notes on Chapter 17 Equations: e = 1.6"10 #19 C This is the fundamental unit of charge. The charge on an electron is -e and the charge on a proton is +e. We never see objects that have a charge which is not a whole number multiple of this number. k = 9 "10 9 Nm 2 2 This is Coulomb s Constant. It is a fudge factor necessary to make C the next equation down give force units in Newtons when the charges are in Coulombs and the distance between the charges is in meters. $ 0 = 8.85 "10 #12 C 2 2 This is the permittivity in a vacuum, a needlessly complicated N "m name. Like Coulomb s Constant it s a fudge factor to make the units line up correctly. Units can get pretty tricky and unintuitive in Electricity and Magnetism. PE electric = q%v This is the equation for the Electric Potential Energy of a point charge (q) moving some change in voltage, %V. Physics Ch.17 Study Guide page 1 of 5

2 "V = #Ed This equation is only valid for uniform electric fields. The voltage between two points in a uniform electric field is equal to the strength of the field times the distance between the two points. Here it is important to note that d is only the distance parallel to the electric field. It takes no energy to move a charge perpendicular to an electric field. V = kq This is the voltage of a point that is a distance (r) away from a point charge (q). r Typically, what we really want to know is the change in the Voltage. So, you have to find the voltage at two different points and take the difference. C = $ 0A d A capacitor is generally two metal plates that each have an area (A) and are separated by a distance (d). C is the Capacitance of the capacitor, or, in simpler terms, a measure of how big the capacitor is. $ 0 is described above. C = Q V The capacitance of a capacitor (C) is also equal to the charge (Q) on the capacitor divided by the voltage (V) across the capacitor. PE capacitor = 1 2 QV The potential energy on a capacitor is one-half of the charge (Q) on the capacitor times the voltage (V) across the capacitor. I = "Q Electric Current (I) is measured in Coulombs per second. So, it is the charge "t flowing through a wire (Q, measured in Coulombs) divided by the time (t) measured in seconds. R = "V The resistance of an object (R) is measured in Ohms (%) and is equal to the I Voltage across the object (V) divided by the current through the object (I). P = IV The power in an electric circuit (P, measured in Watts (W)). Is equal to the Current in the circuit (I, measured in Amps (A)) times the Voltage (V). Physics Ch.17 Study Guide page 2 of 5

3 Note on Units: E, electric field, is measured in Newton s per Coulomb (N/C). V, voltage or potential difference is measured in Volts (V). PE, Potential Energy is just energy, it s measured in Joules (J). q or Q, electric charge, measured in Coulombs (C). d, distance is measured in meters. A, area is measured in square meters. C, Capacitance, is measured in Farads (F). I, electric current, is measured in Amperes, also knows as Amps, (A). R, electric resistance is measured in Ohms ("). P, power, as always is measured in Watts (W). Physics Ch.17 Study Guide page 3 of 5

4 Worked Example #1: What is the electric potential difference between a point 1.00 meters away from a charge of 4.50 mc and a point 3.00 meters away from the same charge? What is the energy required to move an electron between these two points? Your Try #1: An electron gains 2.3 x J of energy when it moves from a point 10cm from a second charge to a point 20cm from that charge. What is the value of the second charge? Physics Ch.17 Study Guide page 4 of 5

5 Worked Example #2: A circular parallel-plate capacitor has a diameter of 3.80 cm, and the plates are separated by 1.00 mm. The capacitor stores a charge of pc. a) What is the potential difference across the plates of the capacitor? b) What is the magnnitude of the uniform electric field in the region that is located between the plates? Your Try #2: A parallel-plate capacitor has an area of 5.00 cm 2, and the plates are separated by 1.00 mm. The capacitor stores a charge of pc. a) What is the potential difference across the plates of the capacitor? b) What is the magnnitude of the uniform electric field in the region that is located between the plates? Physics Ch.17 Study Guide page 5 of 5

6 Physics Chapter 17 Your Try Problems (Based on various worked examples.) 3) Video 17j: Locate the value of the resistivity of aluminum, and calculate the resistance of an aluminum wire that is 132 meters long with a diameter of 0.25 mm. 4) Video 17k: Calculate the current in the aluminum wire from the previous problem if it is connected to a 12V battery. 5) Video 17k: Calculate the power used up by the aluminum wire in the previous problems.

7 Answers to Chapter 17 Your Try Problems Worked Example 1: An electron gains 2.3 x J of energy when... Q = 0.32 nc Worked Example 2: A parallel-plate capacitor has an area of... a) V = 90.4 V b) E = V/m or N/C 3) Video 17j: Locate the value of the resistivity of aluminum, and calculate... (! = 2.82E-8"/m) R = 75.8 " 4) Video 17k: Calculate the current in the aluminum wire from... I = 0.16 A 5) Video 17k: Calculate the power used up by the aluminum... P = 1.9 W

8 Name: Physics Chapter 17 Core Problems 1) A proton is show in an electric field in the diagram below. The proton will gain the most Electric Potential Energy if it is moved to point: B C A + D a) A b) B c) C d) D e) C and D are equivalent. 2) A capacitor is made from two circular plates, parallel to each other, and separated by a gap of air. What change would double the capacitance of the capacitor? a) Double the diameter of the plates. b) Double the distance between the plates. c) Either a or b. d) Halve the distance between the plates. e) Halve the diameter of the plates. 3) A copper wire has a certain length, diameter and resistance. What change would give you the lowest resistance. a) changing the material from copper to iron, but leave the dimensions the same. b) make the diameter half of the original, leave the length and the material the same. c) double the length but leave the diameter and material the same. d) double the diameter but leave the length and the material the same. e) cut the length in half but leave the diameter and the material the same. 4) What is the electric potential difference between a point 1.00 meters away from a charge of 4.50 mc and a point 3.00 meters away from the same charge? What is the energy required to move an electron between these two points? 5) 1 mole (6.02 x ) electrons flow through a wire in one minute. The wire has a resistance of 12!. a) What is the current in the wire? b) What is the voltage difference between the two ends of the wire? Physics Ch. 17 Core Problems page 1 of 2

9 6) A parallel-plate capacitor has an area of 8.50 cm 2. The potential difference accross the capacitor is 25 V. The capacitor stores a charge of pc. a) What is the separation between the plates of the capacitor? b) What is the magnitude of the uniform electric field in the region that is located between the plates? 7) A resistor has a resistance of 1.00 M!. It is connected to a 9V battery. a) What is the current through the resistor? b) How much power does the resistor draw? 8) The headlights on a car are rated at 80.0 W. if they are connected to a fully charged 90.0 Ah, 12.0 V battery, how long does it take the battery to completely discharge? Physics Ch. 17 Core Problems page 2 of 2