Problems with sliding rheostats, how to use sliding rheostats?

In fact, sliding resistors is not very difficult.

Let me tell you this, the longer the wire, the greater the resistance? This is a concept in the book. Next, you need to know that the sliding rheostat is to change the length of the resistance wire to change the size of the resistance, and finally to achieve the effect of changing the current, is this understandable?

Then you have to know that there is a metal rod on the slide resistor, its function is that the wire resistance can be recorded as 0, when we connect the resistor "one up and down", you have to look at the length of the resistance wire in the circuit to determine the size of the resistance, not look at the length of the metal rod, the closer the slide is to the binding post below, the smaller the resistance, because the length of the resistance wire is small, and vice versa, the resistance is the largest. (ll do you understand this?,If you don't understand, you can still ask.,You can also find your teachers and classmates to solve it.,I wish you a smooth study).

In a series circuit, when the resistance of the sliding rheostat increases, the current in the circuit decreases;

In a parallel circuit (the rheostat is connected in parallel with the consumer), when the resistance of the sliding rheostat increases, the current in the dry circuit decreases;

In hybrid circuits, specific problems need to be analyzed on a case-by-case basis.

To solve this kind of problem, you need basic knowledge: first, to be familiar with Ohm's law, and second, to the current, voltage, and resistance characteristics of series-parallel circuits.

From Fucheng Creative's blog.

The greater the resistance, the smaller the current and the greater the voltage.

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 the ammeter, the main reason for the error is the lifting 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 connection scheme of the ammeter, the main reason for the error of Yudong is the partial voltage 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.

In circuits, sliding rheostats have a lot of silly effects. In the circuit connected in series by the sliding rheostat, the resistance of the accompanying circuit can be changed, so as to change the voltage division of each component in the circuit, and at the same time, it can also be used to protect the circuit.

The correct connection method of the sliding rheostat is shown in the following figure

Analysis: current limiting connection, in this connection, only part of the sliding rheostat is connected to the circuit, and the other part is short-circuited, in which the exposed part of the access circuit (that is, the part where the current flows), and the resistance of the sliding rheostat to the wide annihilation circuit increases and decreases with the exposed part. When the physical connection is made, you only need to connect one and two binding posts.

The principle of selecting the connection method of the sliding rheostat1. It is required that the voltage at both ends of the measured resistor starts from zero when it is re-sold, and the voltage divider connection method must be selected.

2. In the experimental instruments provided, if the range of the meter is too small or the maximum allowable current of the resistance is too small, the sub-crimping method should be selected.

3. If the maximum resistance of the rheostat is much smaller than the resistance of the measurement circuit, that is, R transformer 4, R transformer is similar to R measurement, and both voltage division and current limiting are available, considering that the energy consumption is small during current limiting, the current limiting connection method should be selected.

Method 1 In the circuit, there are two applications:

One is partial pressure, and the other is current limiting. That is, in the series circuit, the resistance value of the resistance can be adjusted to limit the current in the circuit, and the resistance can also be adjusted in the parallel circuit to adjust the voltage at both ends of the electrical appliance (that is, the role of the voltage divider). In addition, it should be noted that sliding rheostats are generally only used in laboratories, but are generally not used in actual circuits.

The reason is that due to its thermal effect, it not only consumes more electric energy in the work, but also produces excess heat, which affects the normal operation of electrical appliances; In the actual circuit, it is used to regulate the voltage and current of electronic components such as transformers, inductance coils, silicon control tubes, capacitors, etc. Method 2 In the voltammetry measurement of resistance, the sliding rheostat should reach the maximum value before closing the circuit. As for whether to adjust to the left or to the right, it depends on the connection method of the sliding rheostat access circuit.

When using a sliding rheostat, you should pay attention to the following two things:

1. The wiring should be "one up and one down" (not the two above binding posts (equivalent to the wire) and the two lower binding posts (equivalent to a fixed value resistance) at the same time);

2. Before closing the switch, the resistance value should be adjusted to the maximum place (i.e., the position where the current is minimized) (purpose: to protect the circuit).

It is related to the connection of the wire, the resistance value of the 2 binding posts above is 0, and the resistance value of the 2 below is the same as the maximum no matter how you move the slide blade, and it can not be changed to the resistance when you can change the resistance, you need to see the length of the resistance wire connected to the circuit, the longer the resistance, the greater the resistance.

The principle of sliding rheostat resistance change: "far big and near small" - the farther the distance between the slide p and the lower binding post, the greater the resistance, and the closer the resistance, the smaller the resistance.

Because the resistance of the measured resistor does not change.

The voltage of the sliding rheostat increases with the increase of the vertical resistance, so the current decreases, and the voltage of the measured resistor decreases, and the current is also high.

This is my understanding.

Sliding rheostat: Changed by changing the length of the resistance wire of the access circuit.

The size of the resistance of the variable access circuit part, which is related to the above principle.

Consistently, the sliding rheostat changes the electricity connected in the circuit.

resistance length to change resistance.

Ohm's law: i = u r

The derivation of the residual disturbance r=u i, the application of this formula should.

It is important to note that Ohm's law is only a qualitative calculation of the magnitude of the resistance.

In practice, the resistance does not change depending on the amount of current.

Voltage: The sliding rheostat changes the voltage because the resistance changes.

Ohm's law is the way to know.

In order for the sliding rheostat to be able to play the role of side ridge to change the resistance, the binding post should be connected to the circuit one by one.

If the binding post at the lower end is the left binding post connected to the bending start circuit, the effective resistance is on the left, so the slider moves to the left, the effective resistance length becomes smaller, and the effective resistance becomes smaller; The slide moves to the right, the effective resistance length becomes larger, and the effective resistance becomes larger.

If the binding post at the lower end is the right binding post to access the circuit, the effective resistance is on the right, so the slider moves to the right, the effective resistance length becomes smaller, and the effective resistance becomes smaller; The slide moves to the left, the effective resistance length becomes larger, and the effective resistance becomes larger.

If the sliding rheostat is connected in series with the circuit, the current in the circuit becomes smaller when the effective resistance of the sliding rheostat becomes larger; If the sliding rheostat is connected in parallel with the circuit, when the effective resistance of the sliding rheostat becomes larger, the current in this branch becomes smaller, and the buried current of the other branches is basically unchanged, and the current of the dry circuit becomes smaller.

Look at the binding post under the sliding rheostat, when you select the lower left binding post, the sliding resistance to the right will become larger and the current will be smaller. It is judged by looking at the length of the variable wire in the changed ridge state, and the longer the connected electric Zhenzhou resistance line, the greater the resistance.

Well, the voltage of one dry cell is, and the total voltage of three dry cell cells is.

Because it is connected in series, the resistance ratio is equal to the voltage ratio.

The resistance of the bulb is 6, and the voltage of the maximum range of the voltmeter is 3. So the voltage assigned by the sliding rheostat is.

xx=3。The current in the circuit is divided by (3+6)=, and the ammeter is offset by the midline of the meter dial. The voltmeter pointer is also deflected past the center line of the voltmeter dial. Therefore, the resistance of the sliding rheostat connected to the circuit is 3.

So the resistance to the connected circuit is at least 3.

In the event of a short circuit, the power supply is directly connected to the wires and there is no load.

1: Because if it is connected in parallel on both sides of the power supply, there is a possibility of short circuit, burning the resistor or even the power line.

2: The resistance value is constant after connecting the two ups, and cannot be adjusted; Connecting two times is equivalent to a short circuit, which does not play the role of adjusting the resistance value.

Under normal circumstances, both graphs function the same. But the circuit diagram above, when the sliding rheostat sliding vane is in poor contact.

It can ensure that the circuit continues to be on. The circuit diagram below shows that the sliding rheostat slide is in poor contact.

There is no guarantee that the circuit will continue to be on.