How to distinguish which electrical appliance is measured by the ammeter in the circuit 30

When there are many ammeters in the circuit, the ammeter measures the electrical appliances that are connected in series with the ammeter on a branch road, so the essence of this problem is a circuit analysis problem.

Identify strings. For parallel circuits, the following methods can be used.

1) Current shunt method.

The main point of this method is to start from the positive pole of the power supply and follow the direction of the current until you reach the negative pole of the power supply. No matter how the circuit is bent, as long as the current is not divided, that is, the current flows from one electrical appliance to another electrical appliance and flows all the way, then the electrical appliance is connected in series, and the composition is a series circuit.

If the circuit splits at one point, indicating that there are both trunks and branches in the circuit, then the current will converge at another point after passing through the consumer on the branch, and will return to the negative pole of the power supply. When there are no electrical appliances on the main road, and only one electrical appliance is used on each branch road, these appliances form a parallel circuit.

2) Node method.

For those with strings. For students with preliminary knowledge of parallel circuits, it is easy to see the connection method of electrical appliances from the standardized circuits. But when faced with an unregulated circuit, especially when the wires in the circuit are cross-connected in multiple places, beginners tend to be confused.

The "nodal method" can be used to identify such circuits. Nodes are those points in a circuit where the wires are "cross-connected", including shunt and bus.

The simple example is that the water meter in your home shows your home, and other people's homes display their own.

It depends on which appliance or appliances the ammeter is connected in series.

Equivalent to a wire. An ammeter is the equivalent of a wire in a circuit, and a voltmeter is equivalent to an open circuit in a circuit.

Under normal circumstances, we think that there is no voltage on the wire, in fact, there is voltage on the wire, but because it is very small, so it is regarded as no voltage, in the first series circuit voltage law experiment, we get the law is that in the series circuit, the sum of the voltages at both ends of the electrical appliances is equal to the total voltage. It can be seen that the resistance of the wire is indeed not considered.

Precautions for the use of ordinary ammeters.

1. The ammeter should be connected in series in the circuit.

2. The appropriate range should be selected according to the size of the measured current. For the ammeter with two ranges, it has three terminals, and when using, it is necessary to see the range mark of the terminal clearly, and connect the common terminal and one range terminal in series in the circuit under test.

3. When measuring DC current, the "+" polarity of the terminal of the DC ammeter should not be wrong, otherwise the instrument may be damaged. Magnetoelectric ammeters are generally only used to measure DC current.

Ammeter. With which appliance to connect in series. It is to measure the current of which electrical appliance. Note that it is the two ends of the appliance that actually measure the current below the voltage.

in series circuits.

, see which electrical appliance the ammeter is connected in series with which electrical appliance to measure the current in which electrical appliance. When connected in series, the current is the same, so the ammeter measures that the bulb current is equal. If in parallel circuits.

If the ammeter is on the main road, it is measured that the current of the bulb on all branches; If measured on a branch road, it is the bulb current on this branch road.

When the circuit is connected in series, the current is equal everywhere, so the electric meter is the voltage of the electrical appliance and the power supply voltage no matter whether it is placed in the first place.

When circuits are connected in parallel, the trunk current is equal to the sum of the currents of each branch.

Therefore, when the ammeter is placed on the trunk circuit, the total current is measured.

And when the ammeter is placed in the branch, the branch is placed in which to measure the current passed by the electrical appliances in the slippery branch.

FYI

The measurement principle of the voltmeter and the ammeter itself is the same, that is, according to the current flowing through the meter head, the pointer is deflected at different angles, and the measured value is obtained according to the scale of the dial.

The actual current passing through the meter is very small, and there is a shunt circuit inside the ammeter, which can reduce the measured large current proportionally and reflect it on the dial. The voltmeter uses voltage division and current splitting to obtain the meter current proportional to the measured voltage, and uses the current to reflect the voltage.

When the opening and closing of the chan rise, the circuit has two branches, the first through the R3 circuit, the second through the R1R2 parallel connection and then series R4 to form a circuit. The voltmeter measures the voltage of the old end of R1R2 in parallel for two acres, and the resistance value of R1R2 is known, then the current of the second branch is I=U R12=1ASince R1=R2, the current flowing through these two is i1=i2=i2= The ammeter measures the current flowing through R1 and R3, so the current of R3 i3= the electromotive force of the power supply E=I3 times R3+R times the total current (i1+i2+i3) E= R4 voltage at both ends U4=E-ri Total-voltmeter reading = R4=2 1=2

After disconnecting the switch, R1R3 is connected in series and then connected in parallel with R4 with the resistor, then the total resistance of the circuit = total current = e total resistance = ,3, first set the ammeter to ignore its internal resistance according to the ideal mode, and the voltmeter is infinite according to the internal resistance of the ideal mode.

1) When the switch is closed, the power supply is equal to being directly added to both ends of R3, while R1 and R2 are connected in parallel, the parallel resistance R12 is 2, and the current flowing through the parallel resistance R12 is 2V 2 = 1A, because R1 and R2 are equal, so the current on each resistor is. In this way, the current flowing through R3 is that the voltage across R3 is 1A*4 = 4V. The current flowing through the power supply is the current flowing through R2 and the current flowing through the ammeter.

2, seems to be missing an r4=? if r4=4:

1)e=;2) 106 15,1, determine which current and voltage are measured by ammeter and voltmeter?

The internal resistance of the power supply r= r1=r2=r3=4 when the switch is closed and the current indication and voltage indication are 2V (1) Q: What is the electromotive force of the power supply? (2) When the switch is disconnected, is the current on the main road more than the hand?

Please specify which currents and voltages are measured by ammeters and voltmeters? This question is not told how much R4 is, or it is simple, and it is better to have a solution process.

Look at which part of the circuit the voltmeter is connected in parallel, it measures the voltage at both ends of that part of the circuit;

Look at which part of the circuit the ammeter is connected to, and it measures the current through that part of the circuit.

In the figure, v is measured to l1

a. Measure the total current.

In the case of ensuring safety, it can be judged by disconnecting the circuit or using the electrical appliance separately.

The principle of ammeter current measurement.

An ammeter is made based on 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, a magnetic field is generated 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. The pointer is deflection.

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.

Generally, it can directly measure the current of the order of magnitude of microamps or milliamps, and in order to measure larger currents, the ammeter should have a shunt resistor (also known as a shunt). It is a measuring mechanism that mainly uses magnetoelectric meters. The resistance value of the shunt should be so that when the full-scale current passes, the ammeter is fully deflected, that is, the ammeter indication reaches the maximum.

For a few amps, a special shunt can be set up in the ammeter. For currents above a few amperes, an external shunt is used.

Ammeter classification.

1 DC ammeter.

DC ammeters mainly use magnetoelectric or electric measuring mechanisms (see mechanical indicator meter measuring mechanisms), the basic measurement of these measuring mechanisms is current, which can be used to directly measure small currents.

2.AC ammeter.

The AC ammeter can use an electromagnetic or electric measuring mechanism. In order to make the magnetoelectric measuring mechanism also used to measure AC current, a rectifier or thermocouple can be used to convert AC to DC first; The electricity meters formed by their combination are called rectifier ammeters (see Rectifier Ammeters) and thermoelectric ammeters.

Precautions when using an ammeter.

Wiring correctly. When measuring current, the ammeter should be connected in series with the circuit under test; When measuring voltage, the voltmeter should be connected in parallel with the circuit under test. When measuring DC current and voltage, it is necessary to pay attention to the polarity of the instrument, which should be consistent with the polarity of the measurement.

Measurement of high voltages and currents. When measuring high voltages or currents, voltage transformers or current transformers must be used. The range of the voltmeter and ammeter should be consistent with the rated value of the transformer. The general voltage is 100V and the current is 5A.

Expansion of the measuring range. When the measured circuit exceeds the range of the instrument, an external shunt or voltage divider can be used, but it should be noted that its accuracy level should be consistent with the accuracy level of the instrument.

In addition, it should also be noted that the use environment of the instrument should meet the requirements and be kept away from the external magnetic field.

There is a pair of magnetic poles in the ammeter, the middle of the pole is a coil, the current to be measured flows through the coil, the coil is rotated under the action of the magnetic field of the magnetic pole, and the reaction spring (called the hairspring) is installed on the shaft, when the rotation force of the coil and the reaction spring force want to wait, the pointer with the shaft stops there, and the current is big.

A resistor with a very small resistance value is connected in series between the two meter pens of the ammeter, and the meter needle is driven to swing according to the voltage difference between the two ends of the resistor.

The main principle of an analog ammeter is that an electric current passes through an electromagnet to generate a magnetic field, and the magnetic field acts to drive the pointer.

Digital ammeters are mostly converted into voltage through resistance, and then converted into digital output through an analog-to-digital conversion chip (AD).