Test3_spring2010key

Test3_spring2010key - Problem 1 (25 Points) A 40 cm long...

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Unformatted text preview: Problem 1 (25 Points) A 40 cm long high-resistance wire with rectangular cross section 7 mm Meter 1 by 3 mm is connected to a 12 volt battery through and ammeter as shown in the figure. The resistance of the wire is 50 ohms, The resis- tance of the ammeter and battery are negligible. Leads to a high— resistance voltmeter are connected as shown, with the - lead to the inner edge of the wire and the + lead connected to the outer edge of the wire at the bottom location C. The distance along the wire between voltmeter connections is 5 cm. (a 3pts) On the diagram, draw the electric field inside the wire at at the 3 locations marked x. (b 3pts) What is the magnitude of the electric field at location B? ihvflzwt ———» 12v: 5101/) E:— JE. : gold/C H 3 mm thick (c 4pts) What does the vol—gmeter read, magnitude and Sign? (d 4pts) What does the ammeter read, magnitude and sign? e \/-0 12 r . I:7Mn/4E :- »-—“ " - ow Rim SOIL (e 8pts) There are 1.5 x 1026 free electrons per cubic meter int he wire, What is the mobility of the material that the wire is made of? M: ,_ liog‘i) we? ’- {Leg/fittgzacmx.oogxgo) (f 3pts) Switch meter 1 from being an ammeter to being a voltmeter. Now What do the two meters read? Problem 2 (25 Points) 0.22 m |‘———*_‘I (a 5pts) A 1.5 volt battery is connected to thick conducting nichrome wire as shown in the diagram. Draw an arrow (at the point marked by the cross on the bottom segment) indicating the direction of the electric field in— side the nichrome wire. Label this E. At this same point, draw two more arrows indicating the direction of electron current (label this 2' ) and the direction of conventional current (la- bel this I) 0.22 m (b 8pts) In the steady state, what is the potential difference VA — VB if the wire has a total length of 0.66 meters, i.e. 0.22 meters on each of the three segments? Express your answer in volts and clearly indicate the sign. Briefly explain your reasoning. Ema Sofiwt has (es/Hume [2 RTOTAL : Q z (C 12pts) NOW suppose we add a second nichrome Wire to the circuit as shown in the diagram. The second wires has twice cross-sectional area and the same length (each of its three segments is 0.22 meters long) as the first Wire. In the steady state, calculate VA — VB. Express your answer in volts and clearly indicate the sign. Briefly explain your reasoning. 0.22 m 0.22 m Problem 3 (25 Points) At a particular instant a proton is moving with velocity <5.5 X 107, 0, 0) m/s, and an electron is moving with velocity <5 X 107, ~5 X 1077 0) m/s. The electron is located 1.5 X 10—6 m below the proton (in the y direction). V /} T- 99—» 5'} E l g : :3. z I 3? Q}. r _L - _‘ (3(0111‘ ofpage) S/ '2 $5 i’ (a 4pts) On the diagram draw an arrow representing the electric field at the location of the electron, due to the proton. Label it Ep. mm (b 4pts) On the diagram draw an arrow representing the magnetic field at the location of the electron, due to the proton. Label it Bp. (c 4pts) On the diagram draw an arrow representing the electric force on the electron at this instant. Label it Fez. (d 4pts) On the diagram draw an arrow representing the magnetic force on the electron at this instant. Label it Fmag. (e 9pts) Calculate the magnetic force on’the electron at this instant. Your answer should be a vector. Show all work. in, E~;<»3.\s 5'18, ~3.|3f'/%;0> N Lv Problem 4 (25 Points) (a 8pts) A capacitor, with separation s,- and unknown area, is connected to a bat— tery through Nichrome wires and is fully charged, with +62,- on the positive plate. I Show the approximate charge distribution :I- 'I I " I I everywhere, and the net electric field in— side the wire at the locations marked with ' ' an X. If any of these quantities are zero, -. ' state this explicitly. (b 8pts) The capacitor plates are quickly pulled farther apart so that the new plate separation is sf. A few nanoseconds later . (the charge on the plates remains un— ,1 changed), show the approximate charge distribution everywhere and the net elec- tric field inside the wire at the locations marked with an X. If any of these quanti- ties are zero, state this explicitly. (c 3pts) After a very long time, is the charge Q f on the positive plate of the capacitor greater than, less than, or equal to Q1"? Explain briefly. e:aav , ‘ Ci EL “:9 H: C goes (bowed Owl AV is Warner-f Q mcsiqlfo 9s 34> QrAQC (d 6pts) What is Q f in terms of the given variables? You may assume that the length of the Wires does not change. Since the area of the capacitor plates is unknown, your answer should not contain this quantity. C :: 4) CG: $0 J Cd; .._—_ 8 8‘2 3g ...
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Test3_spring2010key - Problem 1 (25 Points) A 40 cm long...

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