I-V Characteristics
Organization
Abstract
The experiment aims to provide an insight into the I-V characteristics of some two terminal electronic components in which the components will be setup in a circuit through which voltage will be passed and the resultant current will be measured and recorded. The different components will be found to behave differently under changing voltage and their behavior. The graphs of voltage versus current will be plotted for different components using computer software. The experiment will also allow an opportunity to gain experience in collecting data through computer and setting up simple circuits which can serve as a starting point for advanced circuits. The resultant I-V characteristics will also provide information about the electronic component depending on their behavior in the circuit as the I-V characteristics is an important tool to understand the nature of the electronic component.
Introduction
The present experiment aims to measure current-voltage characteristics of different electronic components. For instance if a potential difference (V) is applied across the terminals of a conductor, then some current (I) will flow through it and it can be said to have an electric resistance R=V/I. IN some cases R remains constant while in general cases, it is not constant and depends upon flowing current or applied voltage. It may also depend on external influences like temperature and others. For non-constant and constant R, IV curve is called current-voltage characteristic of the electronic component.
Description of the Experiment
The present experiment measures I-V characteristics of various electronic components. The voltage applied through the terminals of the electronic components is studies while the resultant current flowing through it is measured leading to plotting of I-V graph. The data is recorded by the PASCO CAPSTONE software on the computer and PASCO 850 universal Interface. The data is recorded in the form of current as a function of applied voltage. The dynamic resistance of the component can be found by Ohm’s law:
The apparatus needed for the experiment includes light bulb, PASCO CAPSTONE Software, Brown-black-brown resistor, Red-red-brown resistor, Thermistor, Photoresistor, Diode, Light Bulb, wires, breadboard, voltage source and Multimeter.
Procedure
Data must be collected for minimum ten seconds to allow a full cycle of triangular output voltage. For thermistor, take two sets of readings. One as warm thermistor and other as cool thermistor. Pinch the thermistor between the finger and thumb for warming it to the body temperature and keep it pinched throughput the data collection. For Photoresistor, take three sets of data as bright, dim and dimmer. Place a piece of paper on the Photoresistor for taking reading of dim Photoresistor and place two pieces of paper for dimmer Photoresistor.
Data and Results
The data was collected for each electronic component and a graph was plotted using the software.
1. Brown-Black-Brown Resistor
The figure 1 shows the graph generated by the software for the Brown-Black-Brown Resistor. As indicated in the graph, the slope of the resistor was found to be 94.3 ± 0.016. The reading from the Multimeter indicated a resistance of 98.3 Ω. The dynamic resistance comes out to be 93.69 Ω. It can be seen that the resistance reading of Multimeter is bigger than the resistance found through graph as Rmultimeter = 98.3 Ω while Rgraph = 94.3 ± 0.016 Ω.
Figure 1: I-V Characteristic of the Brown-Black-Brown Resistor
2. Red-Red-Brown Resistor
The figure 2 shows the graph generated by the software for the Red-Red-Brown Resistor. As indicated in the graph, the slope of the resistor was found to be 213 ± 0.066. The resistance from graph is equal to the slope of V-I graph which is 213 ± 0.066Ω. The reading from the Multimeter indicated a resistance of 198.5 Ω. The dynamic resistance comes out to be 217.02 Ω. . It can be seen that the resistance reading of Multimeter is smaller than the resistance found through graph as Rmultimeter = 198.5 Ω while Rgraph = 213 ± 0.066Ω.
Figure 2: I-V Characteristic of the Red-Red-Brown Resistor
3. Thermistor
Two sets of data are taken for thermistor, one as warm thermistor and other as cool thermistor.
3a Warm Thermistor
The figure 3 shows the I-V graph generated by the software for the warm thermistor. The slope indicated by the graph is 709 ± 1.9 which is equal to the dynamic resistance at one point. The dynamic resistance comes out to be 222 Ω.
Figure 3: I-V Characteristic of the Warm Thermistor
3b Cool Thermistor
The figure 4 shows the I-V graph generated by the software for the cool thermistor. The slope indicated by the graph is 735 ± 2.7 which is equal to the dynamic resistance at one point. The dynamic resistance comes out to be 704.70 Ω.
Figure 4: I-V Characteristic of the Cool Thermistor
4. Photoresistor
Three sets of data were taken for Photoresistor with a varying amount of light incident on it. The different sets were for the bright, dim, and dimmer Photoresistor.
4a. Bright Photoresistor
The figure 5 shows the I-V graph generated by the software for the bright photoresistor. The slope indicated by the graph is 1000 ± 2.5 which is equal to the dynamic resistance at one point. The dynamic resistance comes out to be 898 Ω.
Figure 5: I-V Characteristic of the Bright Photoresistor
4b Dim Photoresistor
The figure 6 shows the I-V graph generated by the software for the dim photoresistor. The slope indicated by the graph is 3190 ± 17 which is equal to the dynamic resistance at one point. The dynamic resistance comes out to be 1672.50 Ω.
Figure 6: I-V Characteristic of the Dim Photoresistor
4c. Dimmer Photoresistor
The figure 7 shows the I-V graph generated by the software for dimmer photoresistor. The slope indicated by the graph is 6830 ± 73 which is equal to the dynamic resistance at one point. The dynamic resistance comes out to be 1778.64 Ω.
Figure 7: I-V Characteristic of the Dimmer Photoresistor
5. Light bulb
The figure 8 shows the I-V graph generated by the software for the light bulb. The slope indicated by the graph is varying which means that the resistance of the component keeps on changing with varying voltage applied. The minimum slope recorded is 60.502 while the maximum is 284.736. The dynamic resistance comes out to be 82.57 Ω. The slope of the graph indicated an increase of resistance with increasing applied voltage. This was due to the temperature rise due to increased flow of current through it which increased the resistance. Similar observation was made when negative potential was applied. It was exactly opposite to thermistor where resistance decreased with increasing temperature.
Figure 8: I-V Characteristic of the Light Bulb
6. Diode
The figure 9 shows the I-V graph generated by the software for the diode. The graph indicates that the diode acts as an insulator for certain range of voltage and as a low resistance conductor after a certain threshold voltage. The dynamic resistance comes out to be 12636.68 Ω. The current was allowed to flow only in positive direction and after a threshold voltage, the diode started to behave like an open circuit. This was due to its semiconductor nature where after the threshold energy is provided to electrons, they start conducting.
Figure 9: I-V Characteristic of the Diode
Analysis and Conclusion
Sample calculation
In case of Brown-Black-Brown Resistor resistor, the indicated voltage applied (V) = 14.616 V while the current at that voltage (I) = 0.156 A.
Since, Rdyn=∆V∆I
Thus, dynamic resistance = (14.616/0.156) Ω = 93.69 Ω.
Analysis
The experiment showed that different electronic components demonstrated different I-V characteristics. Some components showed constant resistance while other showed non-constant resistance. Varying graphs were obtained depicting varying relationships between applied voltage and flowing current.
In case of resistors, the slope was found to be almost equal to resistance as the graph came out to be a straight line. On the other hand, thermistor showed change in resistance with changing temperature. Warm resistor showed less resistance as compared to cold one. This showed that the thermistor was negative temperature coefficient type.
In case of Photoresistor. It was found that it demonstrated decreasing resistance with increasing incidence of light on it as light excites the free electrons that help in conduction of electricity. In case of light bulb, the slope of the graph indicated an increase of resistance with increasing applied voltage. This was due to the temperature rise due to increased flow of current through it which increased the resistance. Similar observation was made when negative potential was applied. It was exactly opposite to thermistor where resistance decreased with increasing temperature.
In case of diode, the current was allowed to flow only in positive direction and after a threshold voltage, the diode started to behave like an open circuit. This was due to its semiconductor nature where after the threshold energy is provided to electrons, they start conducting.
