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In the experiment to explore which factors are related to the resistance of conductor
Material, length, cross sectional area
In the experiment of "exploring which factors the resistance is related to the conductor", we compare the connected resistance by changing the supply voltage under a certain condition
Current
Selection of resistance measuring circuit by voltammetry (Trial contact method)
When the internal connection method and external connection method are selected by touch test method, why does the significant change of voltage indication indicate that the voltage division function of the ammeter is strong? If the significant change of current indication indicates that the voltage division function of the ammeter is strong?
1. The voltmeter changes obviously
One is to measure the voltage at both ends of resistance, the other is to measure the total voltage of ammeter plus resistance
The obvious change of voltage indication indicates that the voltage at both ends of ammeter is comparable with that at both ends of resistor
That is to say, the internal resistance of the ammeter is comparable with that of the resistance to be measured, indicating that the resistance value of the resistance to be measured is close to the internal resistance of the ammeter, that is, the resistance value is smaller, so the external connection method should be used
2. The current indication changes obviously
One is to measure the resistance current, the other is to measure the total current of voltmeter plus resistance
It shows that the resistance value measured by the tape is close to that of the voltmeter, that is, it is very large, so the internal connection method is used
Why to add bias resistor in mic circuit and how to select it
In mic, the electret capacitor converts the sound signal into electrical signal, which is immediately amplified and output by a common source FET. The purpose of adding resistance is to provide a drain bias for the FET amplifier in mic, so that it can work in the saturation region and complete the task of signal amplification, This resistance is also called bias resistance. How much resistance to choose? It depends on the parameters of the built-in FET. If the resistance is not selected properly, the maximum dynamic output range of the amplifier circuit will be reduced. If the resistance is too large, the FET may enter into the unsaturated region; if the resistance is too small, the maximum dynamic output range of the amplifier circuit will be reduced, The following are the performance parameters and test circuit intercepted from a mic finished product specification. The test conditions are that the supply voltage is 2V and the bias resistance is 2.2kohm. Why is it 2.2kohm? The manual says that the maximum current consumption of MIC is 500uA. If RL is 2.2kohm, the output DC bias is about 1V (2.2k x 500U), which is exactly half of the supply voltage 2V, The maximum dynamic range of the positive and negative half cycles of the output signal is equal. Therefore, setting the bias voltage as the midpoint of the power supply can maximize the dynamic range of the output signal. At present, the internal FET used by most mobile mic are equivalent, so the external parameters of the appearance are similar. Therefore, the bias resistance is generally selected at about 2kohm in circuit design
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