• Title: Ohms Law / Linear Resistors 

    Purpose: To measure the resistance of a resistor by several different methods, to learn the proper use of electrical meters, and to verify Ohm's Law.

    Apparatus: Various meters, a variable voltage supply and a carbon composition resistor.

    Procedure: The instructor will explain the operation of the various meters and the resistor color code.

    A. Determine the nominal value of your resistor and its percent tolerance from the resistor's color code.

    B. Measure the resistance of your resistor with a volt-Ohm-meter (VOM).

    C. Measure the resistance of your resistor with a digital readout electronic meter.

    D. Fig. 1 illustrates the proper connection of a voltmeter and an ammeter for the measurement of a resistance and the verification of Ohm's Law. Vary the variable supply voltage and monitor the meter readings. Record readings when the Voltmeter reads the following values: 0.1 V, 0.2 V, 0.4 V, 0.7 V, 1.0 V, 2.0 V, 3.0 V, 4.0 V, 5.0 V.

    E. Repeat step D using a light bulb instead of the resistor.

     

    Analysis:

    A. Compare the results of Procedure parts A and B.

    B. Compare the results of Procedure parts A and C.

    C. Use the data from Procedure part D and make a graph of the voltage across the resistor versus the current through it on linear graph paper. Find the resistance of the resistor from the slope of the graph and compare it with the nominal value from Procedure part A.

    D. Use the data from Procedure part E and make a graph of the voltage across the light bulb versus the current through it on linear graph paper. Compare the graph with the graph from Analysis C. Comment on the application of Ohm’s Law to a light bulb.

     

    Questions:

    1. Is your resistor within its specified tolerance?

    2. Which of the above methods do you believe is the most accurate for determining the true value of a resistor? Why?

    3. Which part of this experiment verifies Ohm's Law? Explain why this is so.

    4. In this experiment you studied linear resistors. Name a common device (or material) which has a resistance that behaves in a nonlinear manner. Do nonlinear resistors obey Ohm's Law?

     

    Theory:

    Ohm's Law: R =V/I

    where 

    R = resistance in Ohms

    V = voltage across resistor in volts

    I = current through resistor in amperes

    Fig.1 ammeter - voltmeter method for measuring resistance

    Resistor Color Codes

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