phys 351 lab 1

# phys 351 lab 1 - Methods(Note the circuits built in...

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Methods (Note, the circuits built in sections A-C are shown at the back of the lab report) In section A-1, a breadboard was wired with two 10kOhm resistors in series, with an ammeter to measure the current. The two resistors were used as a voltage divider and measurements of current and output voltage were measured as input voltage was changed. A graph of the measurements was then made to calculate how close the observed resistance was to the actual resistance. In section A-2, a mystery resister was picked out of a box, and then analyzed using the same voltage divider method used in section A-2. The procedure chosen was to place the mystery resistor in series with the 10kOhm resistor, and to take voltage output measurements across both resistors, and keep a measurement of current as well as input voltage changed. After recording the measurements, the results were graphed and the slopes of the graphs were used to find the corresponding resistances. In section A-3, we measured the values of the Thevenin equivalent circuit. The voltage was measured across a 10kOhm resistor with an input voltage of 15volts. A 15kOhm resistor was then placed across the output voltage terminals, and then a new measurement of output Voltage was measured and hypothesis and observations were recorded. The 15kOhm resistor was then removed, and a measurement of the short circuit current was taken by finding the current through the voltage output terminals. The Thevenin resistance was then measured using Ohms law, and solving R Th =V Th /I SC . After calculating the Thevenin resistance, the Thevenin equivalent circuit for the voltage divider was built, using a resistor closest to the calculated value of R Th . Next a 15kOhm

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resistor was placed in the same manner as it was before to observe if it still behaves the same way. The current was then measured. In section A-4, a new circuit was made on the breadboard. The open circuit voltage was measured through a wire that replaced one of the resistors, which gave the short circuit current. The thevenin equivalent circuit was drawn. Last, the power supply was switched with a 1kHz sinusoidal wave, and two channels of an oscilloscope were used to observe to observe the input wave and the signal on the resistor R L to observe if there was any phase shift. In section B, the effects of a diode were studied. Diodes do not obey Ohms law, but the resistance still depends on voltage. A circuit containing a 10kOhm resistor, a resistor substitution box, a voltmeter to measure current, and a diode were placed in series with a voltage divider across the diode. The input voltage was set at 5 volts. Then the diode was turned around and the effects on the circuit were measured. It is hypothesized that if 5V were placed across the diode in the original configuration the current would go to 0. The resistor substitution box was then used to vary the resistance, while measurements through the voltmeter and across the voltage divider were taken. The measurements were then graphed. Last, a sinusoidal wave of 2.5 amplitude and no offset
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## This note was uploaded on 11/03/2009 for the course PHYS 351 taught by Professor Staff during the Spring '08 term at UNC.

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phys 351 lab 1 - Methods(Note the circuits built in...

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