Speaker A
Greetings. Today, we will conduct a laboratory experiment. Write down the date. Laboratory experiment number three. Topic: Investigation of the electrical resistance of a circuit with a semiconductor diode. Next, write down the objective and equipment. Objective: To verify experimentally how a semiconductor diode operates in a DC circuit. To determine how the current through the diode changes with varying voltage in forward bias. To verify that the diode allows almost no current to pass when the polarity is reversed. This is called reverse bias. Next, write down the equipment. You can immediately see the equipment I have used. So, we have a semiconductor diode, a DC power source, a voltmeter, an ammeter, a slide rheostat, a switch, and connecting wires. We will conduct this lab remotely, meaning I will perform it myself, while you follow along and take readings from the instruments with me. That is, we must record the current for different voltages. You will see these values on the connected instruments. Of course, those who have the opportunity can perform this lab in person at school and see everything with their own eyes. So, let's proceed to the experiment. And before starting, I remind you once again that when performing any laboratory or experimental work, one must strictly follow safety rules and carefully follow the instructions. The measurement and calculation data you see on the screen today should be entered immediately into the table that will appear on the screen shortly. So, let’s first examine the experiment with the semiconductor diode in forward bias. Task one. Draw the electrical circuit diagram according to the figure. You can see this figure on the right. While solving problems, we saw several circuits where a diode was connected. Therefore, those who carefully watched the previous lesson know exactly how to connect it. Forward bias, as you remember, is a connection where the arrow, which can be distinguished in the diode symbol, points from the plus to the minus. Next, task two. Assemble the electrical circuit according to the drawn diagram using the available equipment. As you have all noticed, I have assembled this circuit. Ensure that the diode is connected in the forward direction. Anode to positive, cathode to negative. I have verified and see that I connected everything correctly. Each diode may differ in both appearance and the symbols marked on it. Therefore, it is not always quick and simple to do. Next, task three. Close the circuit. Using the rheostat, set the lowest possible voltage across the diode. Take the first readings of the voltage across the diode and the forward current through it. Of course, you first need to draw the table. I suggest adding two more columns to it because I made more measurements. Eleven, so that the graph is much more accurate. As everyone has already seen, I set the minimum voltage to 0.5 V. My ammeter showed a current of 0.4. And we enter these values into the table. Next is task four. By moving the rheostat slider, gradually increase the voltage across the diode. After each change, measure the voltage U and the forward current. After completing all the tests, open the circuit. But pay attention, there is a warning. The forward current of the diode must not exceed its maximum value. In most cases, this is 0.3. And a higher current can damage the diode. My diode is specifically for rectifying high currents. It can withstand a current of 5 A. Therefore, in this case, I must not exceed 5 A. And the next point. During the experiment, you must perform at least seven measurements. Seven is the optimal number for building a reliable graph. Of course, the more measurements, the more accurately the relationship is reflected and the better the consistency of the experimental data will be. As I said at the beginning, I performed 11 measurements, so the graph will be quite accurate, meaning we will have the true current-voltage characteristic of this diode. And so, we follow carefully and record all data in the table. The second measurement is 1 Volt. The current is 0.27. And, of course, the rheostat does not allow for very precise voltage settings, so everything will be approximate. Therefore, we will have a certain margin of error. Next, we have 1.2 V, which I set, and the current is approximately 0.41 amperes. At a voltage of 1.3 V, the current is 0.44. And at a voltage of 1.4 V, the current reached half an ampere, 0.5. Next, at a voltage of 1.5 V, we have a current of 0.56 amperes. At a voltage of 1.6 V, we have 0.61. And at a voltage of 1.7 V, approximately 0.65. And at a voltage of 1.8 V, 1. A. At 1.9 volts, we have 0.77. And the last value. At 2 volts, the current passing through with forward connection is 0.82. And if you have recorded that, let's move on to task five. Using the table data, plot the graph of the current passing through the diode versus the voltage across it, that is, I versus U for forward bias, as in the sample. This will be the so-called current-voltage characteristic of this diode. Of course, it is best to do this on graph paper, but as a last resort, you can simply use a squared notebook. If you have finished that, there is a second part to this experiment. We will now test the reverse connection of the semiconductor diode. Task one. Change the polarity of the power source connection or turn the diode around so that the diode is in the reverse direction. Anode to minus, cathode to plus. I will turn the diode around. After all, changing the polarity of the source would require changing the polarity on all measuring instruments. That is not very convenient. There, the diode polarity is changed. Next, task two. Close the circuit, smoothly change the voltage across the diode using the rheostat, and observe the ammeter. As you can see, the ammeter shows zero. But let's switch to microammeter mode just for interest. Here you can see that even when changing the voltage, we have small currents, but we can see by the values that they are truly very, very negligible. And based on what you have seen, you need to make a brief observation record, indicating whether the ammeters showed any values after changing the polarity. And if they did show something, was it noticeable or just barely? And finally, you need to record what conclusion follows from this: whether current flows, or hardly flows at all, when the semiconductor diode is reverse-biased. We saw all of this from the second experiment. After recording, let's move on to the conclusion. Formulate a conclusion where you state, first, the operation of which device you investigated in this laboratory work. Second, does this device conduct electric current equally in the forward and reverse directions? Third, what is the nature of the dependence of the current through the diode on the voltage across it when forward-biased? Linear or nonlinear? How is this visible from the I-V graph, that is, the current-voltage characteristic? Write it down. Next, of course, as always, a check question. Task one. The figure shows three electrical circuits A, B, and C with a current source, a light bulb, and a semiconductor diode connected in different positions. Determine in which case the bulb will light up and in which it won't, and explain your answer by showing when the diode is forward-biased and when it is reverse-biased. And how this affects the direction and presence of current in the circuit. We can see in figure C that we even have two diodes. We had a similar task while solving problems. Anyone who doesn't know how to answer can watch the previous lesson. Next, task two. A current of 0.2 A flows through a semiconductor diode in the forward direction at a voltage of 4 V. Determine the electrical resistance of the diode in this mode. A hint is to use Ohm's law for a circuit section, but solve it as a problem, that is, with a short summary. And the third task is also a problem. At a voltage of 6 V, the current through the diode whe
