How to use an ammeter or voltmeter to determine which of these two resistors is bigger

1。Connect the two resistors in series, and then connect the voltmeter in parallel on the two resistors, and the large number is large, and the resistance is large.

2。Connect the two resistors in parallel, and then connect the ammeter in series with the two resistors respectively, the indication is large, the current is large, and the resistance is small.

The reading of the ammeter is to rely on the current to flow through the sampling resistance, and then converted into the sampling voltage value (u i r), the power supply current meter display, the sampling resistance is generally not too large, otherwise the resistance will consume considerable power, resulting in unnecessary waste of electric energy, but also will affect the normal operation of the electrical load, the sampling resistance of the ammeter is generally taken between a few tenths of a few ohms to tens of ohms, depending on the size of the current; The reading of the voltmeter is to obtain the sampling voltage signal by the collocation of two voltage-dividing resistors, and then send it to the voltmeter for display, generally speaking, the value of the voltage-dividing resistance is very large, in hundreds of thousand ohms or more, the value is too small may pull down the line voltage value, and it will also be quite a lot of current on the side, resulting in unnecessary power loss Therefore, the input resistance of the ammeter is much less than the input resistance of the voltmeter

In the circuit, the resistance with a voltmeter measuring the large voltage drop is large; If the current is measured with an ammeter, the resistance is small, and the resistance is large.

I have never seen a voltmeter with a smaller resistance than an ammeter

Power is required. Then connect the resistor and the ammeter in series and connect to the power supply, and the resistance value of the large reading is small.

The question you are asking is not comprehensive.

The larger the internal resistance of the voltmeter, the better, because the greater the resistance, the smaller the current generated by the voltmeter, and the less influence it has on the trunk current;

The smaller the internal resistance of the ammeter, the better, because the smaller the resistance, the smaller the voltage divider effect of the ammeter resistor.

Estimation methods for ammeters and voltmeters:

Voltmeters and ammeters with ranges of 3 V and 3 A have a minimum division of V and A, and the readings are to be estimated to one-tenth of the minimum division, and the estimated readings are 0 9;

The voltmeter with a range of 15 V, its minimum division is V, the error is the same as the minimum division, in volts, the minimum division is 5, the estimated reading is to the standard, there is only one decimal place, the estimated reading is V, and the mantissa may be 0 9;

The range of a hall air ammeter, its minimum division is a, the reading should be estimated to read to the minimum division, that is, less than half a grid is omitted, more than half a grid to be read out by half a grid, the minimum division of 2, estimated to the standard, there are two decimal places, the estimated reading is a, the mantissa may be 0 9.

The internal resistance of the voltmeter can be regarded as infinite in general. Depending on the magnitude and accuracy of the measured current, the internal resistance of the ammeter varies greatly. However, it is generally between tens of microohms and tens of milliohms.

In fact, because the voltage between the two points is basically reflected by detecting the current between the two points, the internal resistance value of the voltmeter has a certain resistance value (the resistance value of the voltmeter), and this internal resistance value is equivalent to the ratio of the voltage value to the current flowing through the voltmeter after a voltage is connected to the two ends of the voltmeter.

Therefore, the resistance of the voltmeter is related to the sensitivity of the voltmeter, the higher the sensitivity, the larger the resistance value, the larger the measurement range, the larger the resistance value.

Analog voltmeter in 10k ohms to several megaohms, algorithm: multiply the sensitivity by the range, such as 25k ohms If you choose the 50V range, the internal resistance of the range is 1000k ohms, that is, 1m ohms. The 10 range is 250 kohms. The internal resistance of the ammeter is very small, a few ohms.

Digital voltmeters are generally large in tens to hundreds of megaohms. The internal resistance of the ammeter is smaller than that of milliohms.

Pointer MF258 10V, 50V in equal proportion, 250V ammeter internal resistance can not be measured directly by ohmmeter, limited tools can not be measured, generally micro ampere meter hundreds of ohms, milliampere meter a few ohms, ampere meter 0A few ohms, the larger the range, the smaller the current distributed by the meter, the more parallel resistance, the smaller the resistance!

Mechanical voltmeter 10k ohms, ammeter 10 ohms.

Digital voltmeter 100 m ohm, ammeter 100 m ohm.

A known resistance RO is also required.

2 voltmeters:

The RO is connected in series with the resistor RX under test, the RO voltage is measured with voltmeter 1, and the RX voltage is measured with voltmeter 2.

Knowing RO, read out UO with a voltmeter, and calculate IO from i=u r.

In a series circuit, io=ix, read out UX with a voltmeter, and calculate Rx from r=u i.

2 ammeters:

The RO is connected in parallel with the resistor Rx to be measured, and the RO current is measured with ammeter 1 and the RX current is measured with ammeter 2.

If RO is known, IO is read out with an ammeter, and UO is calculated based on U=IR.

In a parallel circuit uo=ux, ix is read out with an ammeter, and rx is calculated from r=u i.

The greater the internal resistance of the voltmeter, the better, and the internal resistance of the ideal voltmeter is infinity, which is equivalent to an open circuit, so that no current flows through the voltmeter during measurement.

The smaller the internal resistance of the ammeter, the better, the internal resistance of the ideal ammeter is 0, which is equivalent to a short circuit, so that there is no voltage at both ends of the ammeter when measuring.

An ammeter is an instrument used to measure the current in an AC and DC circuit. In the circuit diagram, the symbol of the ammeter is"Circle A"。

The current value is expressed in "A" or "A.""is a standard unit. It is made according to the action of an energized conductor in a magnetic field by the force of a magnetic field. There is a permanent magnet inside the ammeter, which generates a magnetic field between the poles, there is a coil in the magnetic field, there is a hairspring spring at each end of the coil, the spring is connected to a binding post of the ammeter, between the spring and the coil is connected by a rotating shaft, and there is a pointer at the front end of the rotating shaft relative to the ammeter.

When there is a current passing through, the current passes through the magnetic field along the spring and the rotating shaft, and the current cuts the magnetic inductance line, so it is affected by the magnetic field force, which makes the coil deflect, and drives the rotating shaft and pointer to deflect. Since the magnitude of the magnetic field increases with the increase of the current, the magnitude of the current can be observed by the degree of deflection of the pointer. It's called a magnetoelectric ammeter, and it's the kind we use in our labs.

In junior high school, the ammeter used is generally 0 and 0 3 a.

Voltmeter: It is an instrument for measuring voltage, and the commonly used voltmeter is a voltmeter. Symbol:

v, there is a permanent magnet inside the sensitive galvanometer, and a coil composed of wires is connected in series between the two binding posts of the galvanometer, and the coil is placed in the magnetic field of the permanent magnet and connected to the pointer of the meter by the transmission device. Most voltmeters are divided into two ranges. The voltmeter has three binding posts, a negative binding post, two positive binding posts, the positive pole of the voltmeter is connected with the positive pole of the circuit, and the negative pole is connected with the negative pole of the circuit.

The voltmeter must be connected in parallel with the electrical appliance under test. A voltmeter is a fairly large resistor, ideally thought of as an open circuit. The voltmeters commonly used in laboratories at the junior high school level have ranges of 0 3 V and 0 15 V.

The first line is Resistor.

Line 2 DC current, DC voltage, AC current.

The third line is AC voltage.

Both the second and third lines swap the range to the maximum value of the indication and multiply it by the proportion.

The top one is marked with resistance scale, and if the scale mark is uneven, the reading method is to indicate the magnification.

If the indication is 30, if the magnification is 1, then the resistance is 30 1=30; If the magnification is 100, then the resistance is 30 100 = 3000 = 3k

The middle ones are marked with -, v, and ma, which are used to measure DC current, DC voltage, and AC voltage.

Pay attention to the selected range when reading:

If the range is 1V, then when the deflection is 3 5, the voltage is;

If the range is 5V, then when the deflection is 3 5, the voltage is 3V;

If the range is 25V, then when the deflection is 3 5, the voltage is 15V;

If the range is 100V, then when the deflection is 3 5, the voltage is 60V;

If the range is 5mA, then when the deflection is 3 5, the current is 3A.

The bottom one is generally not used.

Hopefully, thank you.

The top row is the resistor, and the bottom is the current and voltage.

The measuring range of the multimeter is as follows:

Measuring resistance: -- first put the watch rods together to short-circuit, so that the hands deflect to the right, and then adjust the " " zero knob so that the hands point to 0. Then touch the two rods to the two ends of the resistance (or circuit) to be measured, read the reading of the pointer on the ohmic scale (the first line), and then multiply by the number of the file mark, which is the resistance value of the measured resistance.

Measure DC voltage:--First estimate the size of the measured voltage, then turn the transfer switch to the appropriate V range, connect the positive meter rod to the measured voltage "+" end, and the negative meter rod to the measured voltage "-" end. Then the magnitude of the measured voltage is read out according to the number of the block range and the number of the pointer on the scale mark (the second line) of the standard DC symbol "dc-".

Measure DC current:--Estimate the size of the measured current first, then turn the transfer switch to the appropriate MA range, and then connect the multimeter in series in the circuit. Also observe the tick marks marked with the DC symbol "DC".

Measuring AC voltage:--The method of measuring AC voltage is similar to measuring DC voltage, the difference is that there is no positive and negative difference between AC and AC, so when measuring AC, the watch rod does not need to be positive and negative. The reading method is the same as the reading of the DC voltage measurement described above, except that the numbers should look at the position of the pointer on the scale marked with the AC symbol "AC".

When a multimeter measures voltage, current and resistance, the accuracy of the data it displays is determined by the manufacturer when producing the meter, and the specific degree of accuracy can be found in the technical manual of the multimeter.

How far you read (how many digits you read) when measuring a reading depends on what you actually need. For example:

Measure the AC voltage of the mains and read the single digit of the volt;

To measure the DC battery voltage, it is enough to read to one decimal place;

To measure the current, you can generally read the single digit of the current file (A, Ma) you selected;

When measuring resistance, it is generally sufficient to read the single digit of the ohm (up to one decimal place).

More electric meter reading methods, hand-in-hand to teach you to change the magnification, there are not many people who know.

This is usually due to differences in the accuracy and measurement range of the voltmeter. Impedance refers to the sum of resistance and inductance (i.e., inductance) in a circuit and can be measured with an ohmmeter or LCR instrument. If measurements are made with voltmeters with different accuracy, errors may occur, resulting in different impedance values.

For example, a voltmeter with low accuracy may not be able to detect small fluctuations in the circuit, resulting in low measurement results; A more accurate voltmeter can detect these fluctuations more accurately, resulting in a more accurate impedance value. In addition, the measurement range of different voltmeters may also be different, for example, some voltmeters may only measure low impedance values, and errors will occur when the impedance values are high in the high range. Therefore, when choosing a voltmeter for impedance measurement, you should choose the appropriate instrument according to the measurement requirements, and pay attention to whether its accuracy and measurement range meet the requirements.