How to reduce the error of voltammetry resistance measurement?????

There are two main situations for the resistance measurement error of volt-ampere method: 1. Internal connection method, that is, the ammeter is connected to the circuit measured by the voltmeter, and the resistance of the ammeter cannot be ignored at this time, so the measured voltage value is slightly greater than the actual voltage at both ends of the resistance, and the measured resistance value is large. 2. External connection method, that is, the ammeter is connected to the circuit measured by the voltmeter, and the current flowing through the voltmeter cannot be ignored at this time, so the measured current value is greater than the actual current flowing through the resistance, and the measured resistance value is small.

Of course, if it is the actual situation, it may be necessary to combine the internal resistance of the power supply, the resistance of the wire, etc., but high school physics seems to be at this depth, I hope it can help you).

Why is there always a difference in voltammetry resistance?

a) Internal. It means that the ammeter is connected to it, such as:

In this case, since the ammeter also has resistance, it is also divided into voltage, and the current is correct, the voltage is large, and the resistance is large. When the measured resistance is very small, do not use internal connection, because it is possible that the ammeter divides a lot of voltage, and it will not be accurate.

b) External. As.

In this case, since the voltmeter also has current passing through, the current is on the high side, the voltage is correct, and the resistance is on the high side. When the measured resistance is very large, do not use an external connection, because it is possible that only a small part of the current of the ammeter is through the measured resistance, and most of it is through the voltmeter.

To summarize: when the measured resistance is small, use an external connection.

When the measured resistance is large, use internal connection.

Since the measured resistance in junior high school is not large, it is generally connected externally.

The error of the volt-ampere test resistance value mainly lies in the difference between the internal resistance value of the voltmeter and the resistance value of the resistance to be tested, if the internal resistance value of the voltmeter is much greater than the resistance value of the resistance to be tested, the error is very small, it should be within 1%.

Let the resistance to be measured be r, the voltage on it is ur, and the current passing through it is ir; The voltmeter resistor is RV, the voltage on it is UV, and the current passing through it is IV; The ammeter resistor is Ra, the voltage on it is UA, and the current passing through it is IA.

In the internal circuit of the ammeter, UA UR UA, IA IR, the measurement error is that the voltmeter reading is greater than the voltage at both ends of R, and the resistance calculated by R uv ia is larger than the true value. When R>>Ra, U>>UA, i.e., U UV, does not cause much error in the measurement results.

Applications:

Use a voltmeter in parallel to measure the voltage at both ends of the resistor, and an ammeter in series to measure the current strength of the resistance through it. However, since the internal resistance of the meter often has an impact on the measurement results, this method often introduces significant systematic errors.

According to Ohm's law, the current distribution in parallel is inversely proportional to the resistance, and this connection method is suitable for measuring resistance with a small resistance; Connected inside, the ammeter is accurate, but the voltmeter measures the common voltage of the ammeter and the resistance, according to Ohm's law, the voltage distribution in series is proportional to the resistance, this connection method is suitable for measuring the resistance of the larger resistance.

Error analysis: the structure of the voltmeter is that its internal resistance is very large, the voltmeter is connected to the circuit, not an open circuit, in fact, there is a small current will pass through the voltmeter, and the voltmeter will also be shunted.

The structure of the ammeter is that the internal resistance is very small, it is connected to the circuit, and the internal resistance will also divide the voltage. It is precisely because of the shunt of the voltmeter and the voltage division of the ammeter that errors inevitably occur when the voltammetry measures the resistance.

1. In the external scheme of ammeter, the main reason for the error is the shunt of the voltmeter. Due to the shunt of the voltmeter, the current measured by the ammeter is greater than the current actually passing through Rx. When the values of the voltmeter and ammeter are substituted into the formula r=u i for calculation, the measurement result is that the resistance r is small because the current i is large.

2. In the internal scheme of the ammeter, the main reason for the error is the voltage division of the ammeter. Due to the voltage division of the ammeter, the voltage measured by the voltmeter is greater than the actual voltage at both ends of the rx. When the values of the voltmeter and ammeter are substituted into the formula r=u i for calculation, the measurement result is that the resistance r is large because the voltage u is large.

In the actual measurement, when the resistance value we measure is small, it is more appropriate to use the A scheme. Since the lower the resistance of the rx, the smaller the shunt of the voltmeter, so the error is reduced. When the resistance we are measuring is very large, it is more appropriate to use the B scheme.

Since the resistance of Rx is large, the partial voltage of the ammeter is very small, so the error is very small.

Ammeter internal method: the ammeter measurement is accurate, the voltmeter measures the total voltage at both ends of the ammeter and the resistance, according to r=u i, i unchanged, u is larger, r is larger. Ammeter external method:

The voltmeter is accurate, and the ammeter measures the total current of the voltmeter and resistance, U is unchanged, I is large, and R is small.

The so-called "volt-ampere method" is a method of measuring the voltage u at both ends of the resistance with a voltmeter, measuring the current i through the resistance with an ammeter, and then finding the measurement resistance with resistance r = u i according to Ohm's law.

1. The indexing value of the meter is not enough, there are artificial reading errors, and the reading is not accurate.

2. There is internal resistance between the wire and the power supply, and the calculation formula is not included.

3. Ignoring the influence of temperature on resistance.

Since the voltmeter and ammeter used in voltammetry to measure resistance are not ideal type voltmeters and ammeters, the resistance of the voltmeter is actually not infinite, and the ammeter actually has resistance. Therefore, if you want to reduce the error, the internal method is generally used to measure the large resistance, and the external method is generally used to measure the small resistance.

1) When measuring the resistance of the orange random fixed value resistor with the voltammetry field method, the multiple measurements are made to reduce the error 2) At the beginning of the experiment, slide the rheostat before closing the switch.

The sliding blade should be moved to the maximum resistance value to avoid excessive current in the circuit and protect the circuit, followed by adjusting the voltage at both ends of the fixed value resistance;

So the answer is: reduce the error; The spine protection circuit and the voltage at both ends of the fixed resistor are regulated