Electrical sliding rheostat, connected to three binding posts how to understand

This student asked about the three-terminal connection method of the resistor, if you learn the knowledge of short circuit better, you will understand that after connecting the three endpoints, half of the resistance is short-circuited, generally the half of the resistance at both ends is short-circuited, and the actual access is the half-cut resistance at that end, it is inconvenient to draw here, I don't know if I have made it clear?

If the two ends are connected, then the circuit is the whole section of resistance, the same as the fixed resistance.

One is connected to one end and the other is connected to the dicing, so as the dicing moves, the length of resistance between them also changes, so the resistance is variable.

If you connect two upper binding posts and one lower binding post, it is equivalent to connecting one wire. If you connect one upper binding post and two lower binding posts, it is equivalent to a sliding rheostat, that is, it doesn't matter if the lower one is connected or not.

I don't know, I asked the teacher, the teacher said it was for good looks, but high school must draw like this, I was speechless, but it also showed that this question is not important, the teacher's meaning is to say don't care about it, learning this doesn't help much in physics, and I won't ask you why when I do the question, probably that's it, I also struggled for a long time, but then I found out that it was really useless, maybe it was a limitation of high school ability, maybe it was not helpful for Chinese-style learning, at the high school level. So I can only listen to the teacher and know how to draw. Don't get into the nitty-gritty.

There are two binding posts on both sides of the sliding rheostat element, one up and one down, when the circuit is connected, the sliding rheostat logo in the circuit diagram is very vivid, the arrow above corresponds to the sliding blade of the rheostat, the small rectangular box below represents the resistance wire, and the resistance wire on the rheostat is also below.

The length of the access resistance is the distance from the terminal to the slide, and the other connector of the circuit is one of the above two connectors, so that if you want to find the current flow into the terminal, you can see the change of current caused by the change of resistance.

Precautions for the use of sliding rheostats.

Before use, according to the specific specifications of the sliding rheostat, not only the resistance value must be met, but the current must also be less than the maximum allowable current.

Before using the sliding rheostat, you should slide back and forth several times evenly to remove some substances such as dust and dirt on the contact points of the sliding contact.

When using, before the sliding rheostat is connected to the circuit, the current in the resistive control circuit in the connected circuit should be minimized, so as to protect the resistor or power supply and other electrical appliances to be measured.

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.

Let's start with my opinion: look at which binding post is connected below, not the left or right.

The reason why I think this is because the binding post at the bottom determines the effective resistance of the sliding rheostat, or whether the part connected to the circuit is the left or right end.

<> If the binding post is the left end, the left end of the sliding rheostat is the effective part, and the sliding blade p of the sliding rheostat is shifted to the left, and the resistance value is reduced.

If the binding post is the right end, the right end of the sliding rheostat is the effective part, and the sliding blade p of the sliding rheostat is shifted to the left, and the resistance value is increased in resistance.

And the two binding posts above can be connected arbitrarily.

So, in my opinion, no matter what others think, I insist.

In a sliding rheostat, two binding posts are connected at the lower end, and one binding post is at the upper end. If you want to calculate the resistance of a sliding rheostat, you need to understand the following three key parameters:

Total resistance (r): that is, the total resistance at both ends of the rheostat, usually expressed in ohms ( );

Sliding position (x): that is, the distance between the sliding contact and the first binding post at the lower end, usually expressed in meters (m);

Length (L): Refers to the length of the rheostat, usually expressed in meters (m).

From these parameters to calculate the resistance rx at the position of the sliding contact, the following formula can be used:

rx = r (l - x) /l

This formula is a simplified standard formula for general sized sliding rheostats with an accuracy of less than 10%. where R is the total resistance of the sliding rheostat, L is the length of the sliding rheostat, and X is the distance from the sliding contact to the first binding post at the lower end. Jujubes.

For example, if the total resistance of the sliding rheostat is 10k, the length is 100mm, and the distance of the sliding contacts is 20mm, then the resistance rx at the sliding contact position is shown below

rx = r (l - x) /l = 10,000ω ×100mm - 20mm) /100mm = 8,000ω

Therefore, in the above case, the resistance at the sliding contact position is 8k

The sliding rheostat has four binding posts, and there are two connection methods: current limiting: one is connected to the upper binding post and one is connected to the lower binding post; Voltage divider: one is connected to the upper binding post, and the lower two are all connected to the circuit.

R1 is the partial pressure connection.

When the sliding rheostat slides to the right end, the resistance of the entire circuit increases, and the current decreases because the voltage does not change, and the number of current representations decreases.

Similarly, the slider slides to the left, the resistance becomes smaller, and the current becomes larger.

Of the three binding posts, only two need to be connected.

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Hello, I am very happy to answer your question, I have helped you find the answer, after searching, the left and right sides of the sliding rheostat are connected to the wire The one with the arrow on the top is originally used to slide on the sliding rheostat to adjust the resistance, non-external, travel during the epidemic, please be sure to do a good job of epidemic protection. I hope my reply is helpful and I wish you a happy life!

When the sliding rheostat is connected to the three wirings, it is used as a current bifurcation, I drew a diagram, I don't know if it is right or not, let's see.

I'm here with a discussion mentality, and I hope it will be helpful to you.

It depends on the situation, and usually one on the top and one on the other. However, if the rheostat is considered to be a bifurcation from the trunk road to the branch road, it is possible to connect three binding posts. The top one, the bottom two, the dicing should be in the middle, and the current is separated from the two sides.

Depending on the circuit, a sliding rheostat connected to three binding posts can be used to divide or divert voltage.

This student asked about the three-terminal connection method of the resistor, if you learn the knowledge of short circuit better, you will understand that after connecting the three endpoints, half of the resistance is short-circuited, generally the half of the resistance at both ends is short-circuited, and the actual access is the half-cut resistance at that end, it is inconvenient to draw here, I don't know if I have made it clear?

You read that wrong, the above one is down.

It's easy to understand the principle of a sliding rheostat, otherwise we'll tell you now, and you'll probably forget it in a few months.

Look at the picture: the upper binding post on the left and the upper binding post on the right do not pass through the coil, which means that the two of them are the same; The lower binding post on the left and the lower binding post on the right are just separated by the entire coil, and the resistance is the largest at this time, and you think, if you adjust the sliding piece, the resistance at these two ends does not change at all, because the resistance between them is the resistance of the whole coil. For example, if you connect the upper terminal post on the left and the lower terminal post on the right, then the resistance between them is equal to the right part of the slide (bounded by the slide), which is understandable.

Now you can conclude that the resistance at either end of the lower left end and the upper end = the resistance of the left part of the coil, and the resistance of the lower right end and either end of the upper end = the resistance of the right part of the coil.

Connecting the above two binding posts is equivalent to a short circuit in the circuit, that is, there is a large current passing through the circuit; Connecting the following two binding posts is equivalent to a fixed-value resistor to connect to the circuit, and these two wiring methods cannot change the resistance in the circuit, that is to say, the sliding rheostat does not play a role at this time; When connected to the same test, as you said, the same left (right) rheostat works as well, but the resistance value connected to the circuit at this time is the smallest, which will have a great impact on the circuit (such as short circuit).

The direction of adjustment is different, for example, if they are connected to the left and right, the resistance will increase.

It can still play a variable resistance role, and the effect is the same. At the beginning, it is still necessary to hit the invariant slide to the farthest point.

This is the right thing to do, and it can be used. The key is to look at the effect of regulation on the resistance.