What is the half bias rule to measure the resistance on the circuit?

In secondary school physics, the "half-bias method" often refers to measuring the internal resistance of an "ammeter". Thus the "ammeter" can be modified.

A "ammeter" is connected to the circuit and the sliding rheostat is adjusted to make the meter head fully offset. Then use a resistance box and the meter head in parallel, adjust the resistance box, so that the meter head is half offset, and the resistance value of the resistance box is the internal resistance of the meter head.

This is a rough measurement, but in fact, the current in the circuit has changed (increased) after a resistor box is connected in parallel.

When the half-bias method measures the resistance of the ammeter, due to the change of the circuit connection, when the ammeter is connected to the resistance box in parallel, the total resistance of the circuit becomes smaller, the current flowing through the trunk road becomes larger, and the shunt of the resistance box is greater than that of the ammeter, so the measured resistance value is small.

When measuring the resistance of the voltmeter by the half-bias method, the resistance box is connected in series next to the voltmeter to increase the voltage division of the voltmeter + resistance box, and the voltage division of the resistance box is greater than that of the voltmeter when the half-deviation is large, so the measured resistance value is larger.

The half-bias method is a systematic error, and the way to reduce the error can be to make the resistance on the trunk road as large as possible when the half-bias method measures the resistance of the ammeter, so that the total resistance change of the circuit is relatively small when the resistor is connected in parallel, and the error is small.

Half-bias method of voltmeter resistance principle:

Before and after closing the electric bond, the voltage at both ends of the voltage divider trace remains unchanged, and the total current of the circuit remains unchanged, in fact, the total resistance of the electric key disconnection adjustment resistance box circuit increases, the total current decreases, and the voltage of the parallel part of the voltage divider circuit U=E-i(R1+R) increases, and the voltage represents the number U 2 The voltage at both ends of the resistance box is greater than U 2R> and the measured value of Rv Lushancheng is larger.

1. Semi-bias method of ammeter.

The unknown resistance is connected in series with the ammeter, and then in parallel with a resistance box; Start to adjust the sliding rheostat in the circuit to express the current to full deviation, then turn on the branch where the resistance box is located, adjust the resistance box, and make the ammeter half biased, at this time, the resistance box indication is the unknown resistance measurement value; The main principle is parallel shunt.

2. Semi-bias method of voltmeter.

The resistance box (the starting resistance value is zero) is connected in series with the unknown resistance, and the voltmeter is connected in parallel with the unknown resistance, first adjusting the sliding rheostat in the circuit to make the voltmeter fully biased, and then adjusting the resistance box to make the voltmeter half biased, and the resistance value of the resistance box is the unknown resistance measurement value; It is mainly based on the principle of series voltage division.

1. Semi-bias method of ammeter.

The unknown resistance is connected in series with the ammeter, and then in parallel with a resistance box; Start to adjust the sliding rheostat in the circuit to express the current to full deviation, then turn on the branch where the resistance box is located, adjust the resistance box, and make the ammeter half offset. The main principle is parallel shunt.

2. Semi-bias method of voltmeter.

The resistance box (the starting resistance value is zero) is connected in series with the unknown resistance, and the voltmeter is connected in parallel with the unknown resistance, first adjusting the sliding rheostat in the circuit to make the voltmeter fully biased, and then adjusting the resistance box to make the voltmeter half biased, and the resistance value of the resistance box is the unknown resistance measurement value; It is mainly based on the principle of series voltage division.

The following is the derivation of the principle of semi-bias resistor:

Suppose we want to measure an unknown resistor r, we need to connect a known resistor rx in series at both ends of the resistor to be measured and power the entire circuit. We can use a voltmeter (or oscilloscope) to measure the voltage vx across the rx, and an ammeter to measure the current ix on the rx.

According to Ohm's law, the total current of a series resistor is equal to the sum of the currents on the respective resistors. From this we get:

ix+i=v/（rx+r）

where V is the supply voltage of the entire circuit.

According to the law of voltage distribution of series resistors, the ratio of the voltage on Rx to the voltage on the entire circuit is equal to the ratio of the resistance of Rx to the entire circuit. Thus, we can get:

vx/v=rx/（rx+r）

r=rx*（1-vx/v）/vx

This is the derivation of the principle of semi-bias method for measuring the resistance of swift silver circles. Based on the measured values of vx, v, and known resistance rx, we can calculate the value of the unknown resistance r.

It is important to note that in actual measurements, we usually take multiple measurements to improve the accuracy of the measurement, and use the average value to represent the true value of the resistance. In addition, in order to reduce the influence of the internal resistance of the power supply on the measurement results, we usually use high-precision power supplies and measuring instruments, and ensure that the wiring of the measurement circuit is correct and stable.

In summary, the half-bias method is a method of calculating the resistance value by measuring voltage and current, which is derived by using Ohm's law and the law of voltage distribution of series resistance. <>

1. Semi-bias method of ammeter.

The unknown resistance is connected in series with the ammeter, and then in parallel with a resistance box; Start to adjust the sliding rheostat in the circuit to express the current to full deviation, then turn on the branch where the resistance box is located, adjust the resistance box, and make the ammeter half biased, at this time, the resistance box indication is the unknown resistance measurement value; The main principle is parallel shunt.

2. Semi-bias method of voltmeter.

The resistance box (the resistance value of the starting high pants is zero) is connected in series with the unknown resistance, and the voltmeter is connected in parallel with the unknown resistance, first adjusting the sliding rheostat in the circuit to make the voltmeter fully biased, and then adjusting the resistance box to make the voltmeter half biased, and the resistance value of the resistance box is the unknown resistance measurement value; It is mainly based on the principle of series voltage division.

1. Semi-bias method of ammeter.

The unknown resistance is connected in series with the ammeter, and then in parallel with a resistance box; Start to adjust the sliding rheostat rental grip in the circuit to express the current to full deviation, and then turn on the branch where the resistance box is located, adjust the resistance box, and make the ammeter half offset, at this time, the resistance box indication is the unknown resistance measurement value; The main principle is parallel shunt.

2. Semi-bias method of voltmeter.

The resistance box (the starting resistance is zero) is connected in series with the unknown resistance, and the voltmeter is connected in parallel with the unknown resistance, first adjusting the sliding rheostat in the circuit to make the voltmeter fully biased, and then adjusting the resistance box to make the voltmeter half biased, and the resistance value of the resistance box is the unknown resistance measurement value; It is mainly based on the principle of series voltage division.

The half-bias method can measure the resistance.

r is a sliding rheostat.

r0 is the resistance box.

g is the ammeter to be measured.

Resistance. During the experiment, close S1 first, disconnect S2, and adjust R to make the pointer of the galvanometer fully deviated; Then close the air and dress S2, adjust R0 so that the reading of the galvanometer is half of the full scale, at this time, the value of the resistance box is the internal resistance of the galvanometer.

According to closed circuits, Ohm's law and series-parallel circuits.

characteristics when adjusting the voltmeter.

When the voltage is half-offset, the sum of the voltages on R2 and the voltmeter increases (greater than UG), so the actual voltage on R2 is greater than the voltage on the voltmeter and in the middle (greater than UG 2), therefore, R2 RV, i.e., the measured value is greater than the true value.

In the experiment of measuring the internal resistance of the voltmeter by the "half-bias voltage method", as shown in Figure 2, RW is the sliding rheostat, R1 is the resistance box, before closing the switch S, move the sliding rheostat RW slider P to the far right, and adjust the resistance of the resistance box R to zero; Close the s, adjust the resistance of the sliding rheostat RW, so that the pointer of the voltmeter points to the full scale.

Keep p still, adjust the resistance value of the resistance box r, so that the voltmeter pointer points to the ** of the dial, and note the value of r1 at this time. In the RW