physic lab report Resistor Circuits and Characteristic Curves

Resistor Circuits and Characteristic Curves

Purpose: In this lab we will introduce basic circuit analysis with series and parallel resistor circuits using Ohms Law and Kirchhoff’s laws. We will also introduce characteristic curves and diodes.

Introduction: Ohm’s Law is of general use with circuit elements, with parts of circuits, or with whole circuits. The voltage across a circuit element is equal to the resistance (or equivalent resistance) times the current flowing through the element. (V=IR)

Kirchhoff’s 1st Law of Circuits: The sum of voltages around a closed loop is equal to zero.

“Series Circuits”

Is there one equivalent resistor to replace multiple resistors in series? Resistors in series “add”.

Kirchhoff’s 2nd Law of Circuits: The sum of currents flowing through a junction is equal to zero.

“Parallel Circuits”

Is there one equivalent resistor to replace multiple resistors in parallel? Dividing both sides by V0 gives us: . Resistors in parallel “add inversely”.

Kirchhoff’s Laws are important not only because they give us specific ways to analyze circuits, but also because they are consequences of the laws of Conservation of Energy and the law of Conservation of Charge.

Additional information on this topic may be found in your text.

In electronics, a “characteristic curve” is a graph of the current flowing through component vs the voltage applied. By convention, when applicable, high current, low voltage is plotted in quadrant 1, low current, high voltage is plotted in quadrant 3:

Resistors have a linear curve (straight line); Diodes, symbol: , have a non-linear curve. ) have a non-linear curve. Diodes, with their non-linear characteristics, are useful in several specialized applications such as “steering” signals or “rectifying”

Diodes, with their non-linear characteristics, are useful in several specialized applications such as “steering” signals or “rectifying” alternating voltages.

Procedure: Part 1 (Resistor Circuits):

From several resistors measured independently, connect three or more in “series” and measure the equivalent resistance of the resistor network. A “breadboard” may be helpful in connecting the resistors together. (For best results, ensure that the largest value of resistor is no more than ten times the smallest value of resistor within the network.)

Remember: when measuring resistance, nothing should be connected to the resistor(s) other than the Ohmmeter:

Repeat for at least two combinations of three or more resistors. Do the same for the resistors connected in “parallel”.

Also do this procedure with hybrid circuits –- at least two different combinations of three or more resistors connected in series and parallel.

Draw a schematic diagram of your hybrid circuits.

Part 2 (Characteristic Curves):

Using a power supply, resistor, an ammeter, and a voltmeter configured as shown, obtain and plot a “characteristic curve” using Excel for one resistor, one light bulb, and at least one diode. (You will have to reverse the polarity of the voltage applied to the component in order to obtain data for both sides of the graph.) With a diode, there is a “knee” in the characteristic curve where the current changes rapidly with a small change in voltage. A good graph will require more data points in this region.

Analysis: Resistor Circuits: Compare the measured values of the series, parallel and hybrid resistor networks to the values calculated with the “series” and parallel” formulas.

Characteristic Curves: How do the curves differ between the resistor, light bulb and the diode? What is the effective resistance of the diodes in different regions? Are the curves approximately linear in any region? (Note that the slope will be equal to the conductance.)

Lab Evaluation – Please provide feedback on the following areas, comparing this lab to your previous labs: How much fun you had completing this lab; How well the lap prep period explained this lab; The amount of work required compared to the time allotted; Your understanding of this lab; The difficulty of this lab; How well this lab tied in with the lecture. Please assign each of the listed categories with a value from 1-5, with 5 being the best, 1 the worst. Comments supporting or elaborating on your assessment can also be very helpful in improving the future labs.

Date Last Modified 2/24/17 Page Number 6