When the voltmeter measures the voltage at the end of the circuit, why can t it be regarded as the v

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So look at it separately, the power supply, the internal resistance of the power supply, and the resistance. These three are in series, the voltmeter is connected in parallel with the resistor, and in parallel with the power supply and internal resistance, so it can be regarded as the voltage of the measured resistor, or the voltage and the voltage of the internal aid. In order to obtain the voltage of internal resistance, it is necessary to subtract the voltage of the power supply from the voltage measured by the voltmeter.

Voltmeter. It is a series relationship with internal resistance.

Think about the equivalent circuit diagram of the power supply, is there a small "r" next to the power supply symbol, which means that the power supply and the internal resistance are in series, and the voltmeter is connected in series with the internal resistance.

The voltage of the internal resistance is provided by the battery.

Affect the accuracy of the measurement results, the second is to put itMultimeterBurnout.

When a multimeter measures resistance, it is applied to the resistor by applying a current, and then judging the resistance value according to the voltage drop (voltage) of the current across the resistor. That is, the process of measuring the resistance is actually measuring the voltage at both ends of the resistor. If the resistor itself is charged (voltage), the measured voltage does not reflect the resistance value.

When measuring resistance with a multimeter, you need to pay attention to:

Select the appropriate magnification level so that the pointer is as close to the center of the scale as possible to ensure that the reading is accurate. When measuring, the indicated value of the pointer on the scale is multiplied by the magnification, which is the resistance value of the resistor being measured.

Before measuring the resistance, or after changing the different magnification gears, the two meter pens should be shorted, and the zero knob should be used to adjust the zero, and the battery should be replaced when the zero position cannot be adjusted. After the measurement, the transfer switch should be dialed to the highest AC voltage or neutral gear to prevent the meter pen from short-circuiting, resulting in short-circuit discharge of the battery. At the same time, it also prevents forgetting to dial the gear to measure the voltage and burning the meter head during the next measurement.

In this circuit, the voltmeter is connected in parallel at both ends of the sliding rheostat, because although it is a sliding rheostat, the resistance value at both ends of it is fixed. For example, the sliding rheostat is 1000, that is, the resistance value between the two endpoints from left to right is fixed, and the middle tap p can move left and right, if the wiring on the left side of the sliding rheostat remains unchanged, the right wiring is connected to the sliding piece p, and the left and right movement of p means that the resistance value of the rheostat decreases or increases. When p slides slowly from left to right, the voltage reading of the voltmeter slowly decreases from high to low; If the p-terminal of the sliding rheostat is slowly moved from right to left, the voltmeter reading will slowly increase from small to large until it is equal to the battery voltage.

As can be seen from the figure, the moving contact P of the sliding rheostat is empty, idle, and there is no wiring, and the two terminals of the voltmeter are directly connected to the two ends of the sliding rheostat, so the voltmeter measures the fixed voltage.

In the figure, there are two wires on the terminal post of the voltmeter, one is connected to one end of the fixed value resistor, and the other is connected to one end of the sliding rheostat. Then it was connected to the other end of the custom resistor. It appears to be a determination of the total voltage of the brake resistor and the slipwire varistor.

is due to the slide of the rheostat p, which is at the left end of this rheostat. So the entire sliding rheostat was short-circuited. At this time, the voltage is the voltage above the fixed resistor.

After the voltmeter and the sliding rheostat are connected in series and in parallel with the fixed value resistor, because the internal resistance of the voltmeter is very large, the resistance value of the sliding rheostat is negligible, and it can be considered that the voltmeter is directly connected in parallel at both ends of the fixed value resistance, so the value displayed by the voltmeter is the voltage at both ends of the fixed value resistor. However, in the case that the resistance value of the sliding rheostat is very large, and the current resistance value is greater than the resistance value of the voltmeter (this specific resistance value depends on the battery voltage and the resistance value of the fixed value and the error rate of the voltmeter), the voltage measured by it is not the voltage at both ends of the fixed value resistor, and there will be an error, which is lower than the actual voltage at both ends of the fixed value resistor, and with the increase of the resistance value of the sliding varistor, the voltage at both ends of the measured fixed value resistance will gradually decrease.

The internal resistance of the voltmeter is infinite, the current through the sliding rheostat is zero, and the voltage at both ends of the rheostat is also zero. According to the loop voltage law, the voltage at both ends of the voltmeter is equal to the voltage at both ends of the fixed-value resistor.

At this point, the voltmeter is paired with a sliding rheostat.

After series connection, it is connected in parallel with a fixed-value resistor.

In junior high school physics.

, it can be considered that the sliding rheostat is only used as a wire, and there is basically no current passing through this branch.

In high school physics, it can be considered as a hybrid circuit, the voltage of the two branches is equal, and the resistance of the rheostat is negligible because the internal resistance of the voltmeter is very large compared to the sliding rheostat. The voltage of this branch is almost shared by the voltmeter alone.

Therefore, the root root parallel circuit.

The voltage of the voltmeter is equal to the voltage at both ends of the fixed value resistor.

The sliding rheostat is equivalent to a wire and plays a connecting role, while the voltmeter itself has a large resistance, so the voltmeter measures the voltage at both ends of the resistor.

If the slide is moved to the far right, it is the voltage at both ends of the measured resistor.

The voltmeter is connected in series with the slider, so the slider becomes a starling that cannot be called in front of the voltage surface with an internal resistance of approximately infinity, which is equivalent to a wire.

Hello, can not measure, because the voltmeter should be connected in parallel with the measured resistance, so if you directly use the sensitive galvanometer as the voltmeter, the current in the meter is too large, it will burn out the meter, then you need to connect a large resistance in series in the internal circuit of the voltmeter, so that after the transformation, when the voltmeter is connected in parallel in the circuit, due to the effect of resistance, most of the voltage added to both ends of the meter is shared by the resistance in series, so the current through the meter is actually very small, so it can be used normally.

In a parallel circuit, if you measure the voltage at both ends of the appliance, you will measure the road-end voltage, because the difference in electromotive force between these two points is the road-end voltage.

This is because, in a parallel circuit, the difference in electromotive force between the two ends of all appliances is the same. So, if you measure the voltage between the two ends of any appliance, you will measure the voltage at the end of the road.

Internal resistance refers to the internal resistance of the electrical appliance, which has no effect on the voltage at the end of the road. Therefore, in parallel circuits, the voltmeter cannot measure the voltage that has not reached the internal resistance.

If you want to measure the voltage of the internal resistance, you can use a multimeter to measure the current and then calculate the voltage of the internal resistance according to OHM's law. OHM's law goes like this: Voltage (V) = Current (I) Internal Resistance (R).

In the external method, if the resistance value of the voltmeter is known, can the measured value be corrected directly? How to measure the resistance of a voltmeter? How to fix?

In the external method, if the internal resistance of the voltmeter is known, a more accurate voltage value can be obtained by correcting the measured value. The correction formula is: actual voltage = measured voltage * r1 + r2) r2, where r1 is the internal resistance of the power supply to be measured, and r2 is the internal resistance of the voltmeter.

The corrected value is closer to the actual voltage, which can improve the accuracy of the measurement. In order to measure the internal resistance of the voltmeter, a power supply with a known voltage can be used to connect the voltmeter into the circuit, and then measure the total resistance in the circuit and the voltage at both ends of the voltmeter. According to Ohm's law, the total resistance in the circuit can be calculated, so that the internal resistance of the voltmeter can be calculated

r2 = Total Resistance - R1) *Measured voltage voltmeter reading. If it is found that the internal resistance of the voltmeter does not match the specified value, the following measures can be taken to correct it:1

Adjust the calibration knob on the voltmeter so that it shows the readings of Masasen Lee. 2.Add a variable resistor to the wiring of the voltmeter, and correct the reading of the voltmeter by adjusting the value of the resistor.

3.The voltmeter reading is corrected by connecting a known resistor in series or parallel so that it shows the correct voltage value. It should be noted that when carrying out the correction operation, it is necessary to read the manual of the voltmeter carefully and follow the operation steps on the manual to avoid unnecessary damage to the voltmeter.

Solution: (1) When the switch S1 and S2 are closed, R1 is short-circuited, and the voltage is expressed as the power supply voltage.

2) When only the switch S1 is closed, the voltmeter and R1 are connected in series, and the voltage representation number is 3V, that is, the voltage of the voltmeter is 3V, U=UV+U1, the power supply voltage is unchanged, and the voltage at both ends of R1:

u1=u-uv=,i= uv rv= u1 r1,i.e.: 3v rv= , resistance of the voltmeter:

rv=6000ω=6kω．

A: The resistance of the voltmeter is 6k

The voltmeter is not only a measuring instrument, but also a special resistance in the access circuit The resistance of the voltmeter is generally very large, in order to measure the resistance of a voltmeter, a student is connected to the circuit shown in the figure, the power supply voltage remains unchanged, r1 = when the switch s1 and s2 are closed, the voltage is expressed as; Closed solution only: (1) When the switch S1 and S2 are closed, R1 is short-circuited, and the voltage is expressed as , that is, the power supply voltage is.

2) When only the switch S1 is closed, the voltmeter and R1 are connected in series, and the voltage representation number is 3V, that is, the voltage of the voltmeter is 3V, U=UV+U1, the power supply voltage is unchanged, and the voltage at both ends of R1:

u1=u-uv=,i= uv rv= u1 r1,i.e.: 3v rv= , resistance of the voltmeter:

rv=6000ω=6kω．

Answer: When the resistance of the voltmeter is 6k and the switch S1 is used, what is the resistance of the voltmeter?

There is definitely an impact.

A voltmeter is essentially a sensitive ammeter connected in series with a larger resistor.

When measuring, because the resistance r of the voltmeter is very large, much larger than the resistance to be measured, the current through the voltmeter is almost 0, which does not affect the original circuit.

The actual measurement principle is that the indication of the voltmeter (i.e. the measured voltage) is equal to the number of sensitive current representations (current value) in the voltmeter.

i) Multiply the organization of the resistance r in series, i.e.

U=IR Therefore, if you want to connect it with a resistor in series, it is equivalent to an increase in R.

If r is 1000 ohms and the resistance in series is only a few ohms, of course the effect can be ignored. However, if the resistance in series is more than a few hundred ohms, this effect cannot be ignored.