Lab 7 Kirchoff's Rule

# Lab 7 Kirchoff's Rule - Physics 1BL KIRCHOFF'S RULES Spring...

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Physics 1BL K IRCHOFF S R ULES Spring 2009 Page 1 Introduction In this lab we will examine more complicated circuits. First, you will derive an expression for equivalent resistance using Kirchhoff’s Rules. Then you will discuss the physics underlying Kirchhoff’s rules. Then you will practice drawing circuit diagrams from real circuits and vice versa. Finally, you will use Kirchhoff’s rules and your knowledge of equivalent resistance to analyze complex circuits. Pre-lab questions: How to read Resistor Color Codes First, find the tolerance band. It will typically be gold ( 5%) or silver (10%). Starting from the other end, identify the first band - write down the number associated with that color; in this case Brown is 1. Now 'read' the next color. Here it is blue, so write down a '6' next to the 1. (you should have '16' so far.) Now read the third, or 'multiplier', band and write down that number of zeros. (It is called a multiplier band because you are multiplying the first two bands by 10 to the power of the number of the third band.) In this example the multiplier band is Red (2) so the multiplier is 10 2 . The resistor value is 16 x 10 2 ohms or 1600 Ω or 1.6k Ω . If the multiplier band is Gold move the decimal point one place to the left. If the multiplier band is Silver, move the decimal point two places to the left. The tolerance band tells you how close to the stated value you can expect the actual resistance to be. Gold indicated 5% tolerance and Silver indicated 10% tolerance. Therefore, Gold tolerance resistors are between 95% and 105% of the value indicated by the color bands. If the resistor has one more band past the tolerance band, it is a Quality band. The Quality band indicates the failure rate of the resistor when operated at full power. # Color Mnemonic 0 Black Big 1 Brown Boys 2 Red Race 3 Orange Only 4 Yellow Young 5 Green Girls 6 Blue But 7 Violet Violet 8 Gray Generally 9 White Wins 1 st digit 2nd digit x10 ___ Multiplier First digit Second digit Multiplier Tolerance Quality

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Physics 1BL K IRCHOFF S R ULES Spring 2009 Page 2 1. Resistor color codes: a. What is the resistance of a resistor with the band colors Red Red Brown? b. What colors would you see on a 110 Ω resistor? 2. One light bulb is marked “20 W 120 V” and another “60 W 120 V”. This means that each transforms this amount of electrical energy into light and heat per second when plugged into a constant 120-V potential difference. a. Find the resistance of each bulb. When they are seperately connected to 120 V power supply ( i.e. they each have their own battery) which bulb is brighter? b.
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## This note was uploaded on 09/14/2009 for the course PHYS 1BL taught by Professor Anderson during the Spring '08 term at UCSD.

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Lab 7 Kirchoff's Rule - Physics 1BL KIRCHOFF'S RULES Spring...

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