EMI 2a: Moving Rectangular Loops and Uniform Magnet Fields-Voltage... 2

Transcription

1 EMI 2a: Movng Rectangular Loops and Unform Magnet Felds-Voltage... 2 EMI2a RT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage... 4 EMI2a WBT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage... 5 EMI2a WWT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage... 6 EMI2a CCT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage... 7 EMI2a PET1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage... 8 EMI2a TT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage... 9 EMI2a TT2: Movng Rectangular Loops and Unform Magnetc Felds-Voltage EMI2a M/MCT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage EMI2a LMCT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage EMI2a CRT1: Movng Rectangular Loops and Unform Magnetc Felds - Voltage of 13 EMI2a key 6_08_02

2 EMI 2A: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNET FIELDS- VOLTAGE 2 of 13 EMI2a key 6_08_02

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4 EMI2A RT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE The sx stuatons shown below have rectangular wre loops movng nto, through, and out of unform magnetc felds. All of the loops have the same dmensons 4 cm x 6 cm, although ther orentatons vary. The strengths of the magnetc felds vary among the stuatons. All of the magnetc felds pont out of the page, and all of the loops are movng to the rght at the same speed and they contan a 1 ohm resstor that s not shown. Rank these stuatons, from greatest to least, on the bass of the emf nduced across the loop at the nstant shown. A B C D E F Greatest 1 AD 2 3 B 4 F 5 CE 6 Least OR, All sx of these stuatons have zero nduced emf. Carefully explan your reasonng. The nduced emf s based on E=Blvsnq. It s assumed all q are 90. A, C, & D are the strongest B felds wth C havng no net nduced emf A & D should be the same and the largest. E should also have no net emf. B and F are the next strongest B felds wth B havng a larger l and hence larger emf. How sure were you of your rankng? (crcle one) Bascally Guessed Sure Very Sure of 13 EMI2a key 6_08_02

5 EMI2A WBT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE A stuaton nvolvng a rectangular loop of wre and a unform magnetc feld resulted n the graph below. Descrbe a physcal stuaton that could produce ths graph. Emf (V) (S) Tme Explan: One possble answer would be: A rectangular wre loop movng at constant speed s about to enter a unform B wth ts surface area perpendcular to the B. As soon as the wre reaches the B, the nduced emf ncreases from zero to the postve value ndcated n the graph. As the wre loop contnues to enter the B (but before t s completely n the B), the emf s constant. As the tralng cross wre of the loop enters the B, the nduced emf falls to zero. When the loop s completely nsde the B, the nduced emf s zero. As the loop starts to leave the B, the nduced emf goes from zero to the constant negatve emf ndcated n the graph. As the loop s leavng the B, the nduced emf s negatve and constant. As the tralng cross wre of the loop leaves the B, the nduced emf goes from the negatve constant value to zero. 5 of 13 EMI2a key 6_08_02

6 EMI2A WWT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE What, f anythng, s wrong wth the followng stuaton? If somethng s wrong, dentfy t and explan how to correct the stuaton. If nothng s wrong, explan why the stuaton works as descrbed. If a rectangular loop of copper wth a very small resstor s moved nto a regon of unform magnetc feld, there wll be an emf (V) across the resstor n the loop whle the loop s movng nto the feld, but not once t s completely nsde the feld regon. Ths s a correct statement assumng the velocty of the wre loop s not at an angle of 0 or 180 wth the unform magnetc feld. 6 of 13 EMI2a key 6_08_02

7 EMI2A CCT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE Consder the followng statements about the open rectangular loop shown below. Student A: "An open rectangular loop wll have an emf across the gap when movng nto or out of a unform magnetc feld." Student B: "An open rectangular loop wll have an emf across the gap any tme t s anywhere n the regon of the magnetc feld." Student C: "An open rectangular loop wll have an emf across the gap only when movng nsde the feld regon." Student D: An open rectangular loop cannot have an emf across the gap because there s a break n the loop. Wth whch, f any, student do you agree? Student A X Student B Student C Student D None of them Carefully explan your reasonng. Student A s correct. The flux s changng and t s possble to have a potental dfference wthout a current. 7 of 13 EMI2a key 6_08_02

8 EMI2A PET1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE A rectangular loop of wre wth a small resstor(not shown) s connected to a voltmeter. The loop s gong to be moved nto, through, and out of a unform magnetc feld at a constant speed. The plane of the loop wll be perpendcular to the drecton of the magnetc feld. W L v Predct what the readng(s) on the voltmeter wll be from before the loop s n the feld untl t passes completely out of the feld. As the loop moves at a constant speed, there wll be a constant voltage readng as t enters the feld regon. Once the loop s completely nsde the feld the voltage readng wll drop to zero. As the loop leaves the regon, the voltage readng wll be the negatve of ts readng as the loop entered. The voltmeter readng wll drop to zero after the loop has left the feld regon. 8 of 13 EMI2a key 6_08_02

9 EMI2A TT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE There s somethng wrong n the followng stuaton. Identfy the problem and explan how to correct t. A rectangular loop wth a very small resstor (not shown) s moved nto, through, and out of a unform magnetc feld at a constant rate. The plane of the loop s perpendcular to the magnetc feld. W L v The graph of emf (V) across the resstor n the loop versus tme for ths whole tme perod would look as shown n the graph below. Emf (V) loop enters feld regon wthn feld Tme (s) loop starts leavng feld out of feld The graph s ncorrect-the correct one s shown below Emf (V) loop enters feld regon wthn feld Tme (s) loop starts leavng feld out of feld 9 of 13 EMI2a key 6_08_02

10 EMI2A TT2: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS-VOLTAGE There s somethng wrong n the followng stuaton. Identfy the problem and explan how to correct t. A rectangular loop wth a very small resstor (not shown) s moved nto, through, and out of a unform magnetc feld at a constant rate. The plane of the loop s perpendcular to the magnetc feld. W L v The graph of emf (V) across the resstor n the loop versus tme for ths whole tme perod would look as shown n the graph below. Emf (V) loop enters feld regon wthn feld Tme (s) loop starts leavng feld out of feld The graph s ncorrect-the correct one s shown below Emf (V) loop enters feld regon wthn feld Tme (s) loop starts leavng feld out of feld 10 of 13 EMI2a key 6_08_02

11 EMI2A M/MCT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE A square wre loop s movng through a unform magnetc feld, of strength B, at a constant rate v. The loop s fully n the feld, and the loop has sde length of l. Is the calculaton below meanngful or meanngless for ths stuaton? Emf = (v)(b)(l) v Explan fully. The calculaton s meanngless snce the loop s completely wthn the feld,.e., the nduced emf should be zero. 11 of 13 EMI2a key 6_08_02

12 EMI2A LMCT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE A rectangular wre loop wth a very small resstor (not shown) has ts leadng edge just movng nto a unform magnetc feld. The loop has dmensons of L by W, and s movng at a constant speed. W L v Descrbed below are a varety of changes to ths ntal stuaton. (ALL OF THE CHANGES DESCRIBED ARE MODIFICATIONS OF THIS INITIAL SITUATION.) For each change, dentfy how the change wll affect the emf across the loop. The possble effects on emf are: a) It wll ncrease. b) It wll decrease. c) It wll reverse polarty. d) It wll ncrease and reverse polarty. e) It wll decrease and reverse polarty. f) There wll be no effect on the emf. Changes n the stuaton are: 1) The magnetc feld s doubled n strength. A 2) The velocty of the loop s reduced. B 3) The W sde of the loop s trpled n length. F 4) The drecton of the magnetc feld s reversed. C 5) The L sde of the loop s doubled n length. A 12 of 13 EMI2a key 6_08_02

13 EMI2A CRT1: MOVING RECTANGULAR LOOPS AND UNIFORM MAGNETIC FIELDS - VOLTAGE The flux of a conductng wre that s movng nto, through, and out of a regon n whch there s a unform magnetc feld s shown n the graph below. For the tme perod shown n the gven graph, draw the correspondng emf versus tme graph at the rght. Flux Emf tme t 1 t 2 t 3 tme t 1 t 2 t 3 The nduced emf s a constant from t=0 s to t=t 1 snce the slope of the changng flux s constant. The nduced emf after t=t 1 should be zero snce the flux s not changng. 13 of 13 EMI2a key 6_08_02