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# 2 c palmer august 19 2013 28

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Unformatted text preview: Summer Session 2 - C. Palmer August 19, 2013 35   Current I = nAevd   Drift speed J Average I vd = = nAe ne Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 36   What is the drift speed in a copper wire with radius 1.0 mm when the current is 0.050 A? I vd = nAe Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 37   What is the drift speed in a copper wire with radius 1.0 mm when the current is 0.050 A? I vd = nAe   What is the density of charge carriers? Assuming one electron per copper molecule. ⎛ 1 n = NA ⎜ ⎝ Molar Mass Physics 2B - Summer Session 2 - C. Palmer ⎞ ρCu ⎟ ⎠ August 19, 2013 38   What is the drift speed in a copper wire with radius 1.0 mm when the current is 0.050 A? I 28 3 vd = n = 8.49 × 10 electrons/m nAe vd = 0.050 A (8.49e28m )(π (0.0010m ) )(1.602e-19C) −3 2 = 1.2 e-6 m/s = 4.2 mm/hr Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 39 Physics Concept Components Learning Outcome Explain the relationship between voltage and current or charge through these various components. Circuits Components •  Resistors •  Capacitors •  Inductors Calculate the voltage drop across individual components. Recognize the direction of current flow across individual components. Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 40   Resistivity is a measure of how difficult it is to pass current through a material.   Material specific   Empirically found   Traditionally represented by ρ   Conductivity is a measure of how well a material conducts electricity.   Not surprisingly the two are inversely related. 1 σ= ρ Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 41   The actual amount of resistance that a particular piece of material delivers is based on the material properties (resistivity) and the dimensions.   The dimensions   The length, L   Farther to travel increases resistance   The cross-sectional area, A   More potential pathways current reduces resistance   SI Units, Ω, Ohms L R=ρ A Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 42   The resistivity has also dependence on temperature.   Generally, as the temperatures increases the resistance increases.   Below is the linear approximation that will be more correct closer to room temperature.   T0 = 293 K = 20° C   α = coefficient of resistivity, [α] = K-1 ρ = ρ0 (1 + α (T − T0 )) R = R0 (1 + α (T − T0 )) Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 43   A piece of lead has a resistance of 100.00 Ω at 20° C.   When the temperature is 120° C, what is the resistance?   αPb = 0.0039 K-1 A)  61.00 Ω B)  99.61 Ω C)  100.39 Ω D)  103.90 Ω E)  139.00 Ω Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 44   A piece of lead has a resistance of 100.00 Ω at 20° C.   When the temperature is 120° C, what is the resistance?   αPb = 0.0039 K-1 A)  61.00 Ω B)  99.61 Ω C)  100.39 Ω D)  103.90 Ω E)  139.00 Ω R = R0 (1 + α (T − T0 )) = 100.00Ω (1 + 0.0039 (100 )) = 100.00Ω (1.39 ) = 139.00Ω Physics 2B - Summer Session 2 - C. Palmer August 19, 2013 45...
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