banzhichuan_physics 222 Lab Report_DCR

banzhichuan_physics 222 Lab Report_DCR - V=1.4v d=0.84 mm...

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Zhichuan Ban Physics 222 Lab Li Bing 2/22/2016 DCR Lab Report 1. Question of the day: what is the relation between the voltage to a resistor and the current through it? How does this depend on the material of the resistor? A: the ratio of the voltage to the current is a constant which equal to the resistance of the resistor. Different materials have different resistivity. Less resistivity the materials have, less the ratio of the voltage to the current is. 2. Activity 3: resistivity a. Set up: in this part, we try to identify the material used in rheostat. Connect rheostat with the ammeter, and connect voltmeter with rheostat and ammeter in a parallel circuit. Keep the voltage constant in the circuit, and change the rheostat into 75 turns, 100 turns, 175 turns, 200 turns, 250 turns. Record the current by reading the ammeter. Put data into program and make a line. b. Data: Data we got is shown below: N I/A 75 11.36 100 14.285 175 23.258 200 26.3157 250 32.258
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Unformatted text preview: V=1.4v d=0.84 mm D=52.7 mm c. Data analysis: According to the Ohm’s law, we know V = I ∗ R . In this part, specifically V = I ( R + R A ) . Consider the rheostat is a wire resistor rolled in to a cylinder. And we know R = ρL A . Therefore, substitute into equation V = I ( ρπDN A + R A ) , where D is the diameter of the cylinder, N is the turn on the cylinder, and A is the area of the wire. Change the equation little bit 1 I = πρD AV ∗ N + R A V . This equation suit the graph we got. Consider 1 I as y, and N as x. Then πρD AV would be the slope. D is 0.0527m, and slope of the line is 8.360. Therefore, we can find the ρ is 41 ∗ 10 − 8 . Comparing this number to the resistivity table, it is close to manganin alloy’s resistivity 48 ∗ 10 − 8 . So we can say the material in rheostat is manganin alloy. d. Conclusion: the material used in the rheostat is manganin alloy. e. Calculation....
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