How to change the length of the resistance wire in a sliding rheostat

If the insulating paint falls off and the wires touch, the current will pass over the coil and go directly to the contact site, which will be equivalent to shortening the resistance wire.

The length of the resistance wire is generally not easy to see directly, and now it is generally a resistance box and a rheostat, which can be read directly.

It's not that the insulation layer is hung up, it's because the part that actually participates in the conduction becomes shorter, for example, if you train from the middle of the wire, only half of the actual conductive part is done.

The total length of the resistance wire does not change.

In the process of using the sliding varistor, the movement of its sliding blade is used to change the length of the effective resistance wire of the access circuit (such as the upper metal rod and the lower end), so as to achieve the effect of changing the resistance of the access circuit.

1.When used, the current in the circuit is changed by changing the length of the resistance wire connected to the circuit.

2.(1) The insulation layer is intact, and the current is coiled (that is, it travels along the resistance wire).

2) The insulation layer is scraped off, the adjacent resistance wire is short-circuited, the current advances in a straight line, and the sliding rheostat is equivalent to a "resistance barrel".

4 is metal, which is considered to have no resistance. 3 is regulated, and the longer 4, the smaller the resistance.

It is only possible that the resistance wire is worn, the cross-sectional area has changed, and the measured resistance value has also changed accordingly.

A sliding rheostat changes the resistance by changing the length of the resistance wire connected to the circuit.

The key to seeing the resistance of a sliding rheostat become larger or smaller is to see the change in the length of the resistance wire connected to the circuit.

The resistance wire in the access circuit becomes longer, and the resistance becomes larger. When the left terminal post is connected below, the effective resistance of the access circuit is on the left. Moving to the left, the length of the resistance wire into the circuit becomes shorter and the resistance becomes smaller.

As you move to the right, the length of the resistance wire into the circuit becomes longer and the resistance increases.

When the right post is connected below, the effective resistance of the access circuit is on the right. Moving to the right, the length of the resistance wire into the circuit becomes shorter and the resistance becomes smaller. As you move to the left, the length of the resistance wire into the circuit becomes longer and the resistance increases.

To put it simply, move the terminal post closer to the next connection, and the resistance increases. Move the terminal post away from the direction of the connection, and the resistance becomes larger.

Main introduction

A sliding rheostat is a circuit element that can change its resistance to control the circuit. In circuit analysis, a sliding rheostat can be used either as a fixed-value resistor or as a variable-value resistor. The composition of the sliding rheostat generally includes five parts: binding post, sliding vane, resistance wire, metal rod and porcelain cylinder.

The resistance wire of the sliding rheostat is wound around an insulating porcelain cylinder, and the resistance wire is coated with an insulating layer on the outside. There are three different forms of variation, the X-type is a straight line, and its resistance varies uniformly according to the angle. It is suitable for voltage division, current regulation, etc.

For example, the field frequency adjustment is made in the TV. The Z type is exponential, and its resistance varies exponentially according to the rotation angle, and it is commonly used in volume adjustment circuits. Due to the auditory nature of the human ear's loudness of sound, it is close to a logarithmic relationship.

Select the specifications of the sliding rheostat First, look at the rated voltage of the sliding rheostat, the voltage added to both ends of it should be less than its rated voltage (otherwise it will burn out) Second, look at the rated current, the current in the circuit can not be greater than its rated current (otherwise it will burn out) Third, look at the maximum resistance. The maximum resistance of the sliding rheostat should be greater than or equal to the resistance value required in the specific problem, and the resistance value required in the specific problem should be selected according to the specific problem.

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.

The way to see the resistance of a sliding rheostat become larger or smaller is to judge by observing the brightness of the small bulb in the circuit.

When the slider is moved to the right, the bulb will dim, indicating that the resistance of the sliding rheostat increases. The slide is also shifted to the right, and the light bulb will brighten, indicating that the resistance of the access circuit has become smaller. After the sliding rheostat is connected, the resistance size can be adjusted through the middle contact, and the length of the resistance wire can be changed, so as to change the resistance size.

If the longer the resistance wire, the greater its resistance value, and the shorter the resistance wire, the smaller the resistance value.

When connecting the sliding rheostat, it is necessary to connect the upper and lower wires, and do not connect the two wires at the top or bottom at the same time. If it is connected to the top, it represents a wire with no resistance, while the bottom of the connection represents a fixed resistance value, which does not play the role of a sliding rheostat.

Precautions for the use of sliding rheostats:

1. Before using the sliding rheostat, it is necessary to confirm the maximum resistance of the key and the maximum circuit that is allowed to pass through. During the measurement process, try to make sure that the measured current value is within the range of its maximum range, so as to ensure sufficient safety.

2. When the sliding rheostat is in use, it is also necessary to dial the sliding blade on the lower rheostat back and forth, in order to clean up the dust stains on the rheostat, so that the contact of the sliding rheostat is closer. In addition, in order to protect the sliding rheostat, it must be adjusted to the maximum position before the measurement can begin.

3. When closing the switch of the sliding rheostat, it is necessary to adjust the resistance value to the maximum state, so that the current value in the circuit is smaller, which plays the role of protecting the sliding rheostat, and at the same time, it is not easy to burn out the circuit.