Assignment 08

# Assignment 08 - Class PEP112S2007 Assignment 8 Assignment...

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Class PEP112S2007 Assignment 8 Assignment is due at 11:00pm on Sunday, March 25, 2007 Credit for problems submitted late will decrease to 0% over the course of 10 hour(s) after the deadline has passed. The wrong answer penalty is 1% per part. Multiple choice questions are penalized as described in the online help. The unopened hint bonus is 1% per part. You are allowed 10 attempts per answer. Resistance from Microscopic Ohm's law Your task is to calculate the resistance of a simple cylindrical resistor with wires connected to the ends, such as the carbon composition resistors that are used on electronic circuit boards. Imagine that the resistor is made by squirting material whose conductivity is into a cylindrical mold with length and cross-sectional area . Assume that this material satisfies Ohm's law. (It should if the resistor is operated within its power dissipation limits.) Part A

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What is the resistance of this resistor? Hint A.1 General approach Hint not displayed Part A.2 Microscopic Ohm's law Part not displayed Part A.3 Find the voltage from the electric field Part not displayed Part A.4 Find the current from the current density Part not displayed Hint A.5 Ohm's law for the resistor Hint not displayed Express the resistance in terms of variables given in the introduction. Do not use or in your answer. ANSWER: = Real resistors vary tremendously in overall size. The larger the size, the more power the resistor can dissipate without heating to the point that it is dangerous to nearby components or that the material of which it is constructed begins to change its conductivity (i.e., so that the resistance would no longer be constant). The amount of resistance is determined by the conductivity of the material of the resistor, which can vary over more than 20 orders of magnitude. Commercially available resistors vary from 0.1 ohm or less to more than ohm. PSS 31.1: Four Is a Crowd
Learning Goal: To practice Problem-Solving Strategy 31.1 for problems involving resistor circuits. Find the currents through and the potential difference across each resistor in the circuit shown on the diagram . Use the following values: = 12.0 , = 15.0 , = 45.0 , = 25.0 , and = 25.0 . MODEL: Assume that wires are ideal and, where appropriate, that batteries are ideal. VISUALIZE: Draw a circuit diagram. Label all known and unknown quantities. SOLVE: Base your mathematical analysis on Kirchhoff's laws and on the rules for series and parallel

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resistors. Step by step, reduce the circuit to the smallest possible number of equivalent resistors. Determine the current through and potential difference across the equivalent resistors. Rebuild the circuit, using the facts that the current is the same through all resistors in series and the potential difference is the same for all parallel resistors. ASSESS:
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Assignment 08 - Class PEP112S2007 Assignment 8 Assignment...

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