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Right from the early days of physics, we have heard a lot about the variable. So what is the variable? What function does the resistance have? How is it applied in reality? There are many questions around this device. To be able to answer these questions, Mầm non Cát Linh invites you to find out the article below!

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What is a variable?

Simply understanding the resistance is a pure resistance that can change the value according to the user’s wishes.

They are often used for the purpose of adjusting the operations of the circuit or in changing the control resistance level of the device and phenomenon.

The resistance of the device may be changed by changing the length of the wire or maybe by the impact on the temperature, light or electromagnetic radiation, …

The resistance has an Ohm (Ω) unit, which is named after Georg Simon Ohm – German physicist.

In electrical circuit diagrams, there will be separate symbols from which it can make the process of viewing and research easier. And the symbol of resistance is the same, specifically the symbol of the resistance in the circuit includes the following forms:

Structure and operating principle of resistance

Structure of resistance

Seen from the outside, we can easily see the structure of the transformer quite simple and have 3 main parts as follows:

The coil is made of alloy with large resistance.

The run/foot runs: Ability to run along the coil, changing the value of impedance.

There will be three legs in the circuit (three poles) connected to the circuit. There will be two poles fixed at the top of the resistance and made of metal. The remaining polarity will move and often called the lever can change the resistance in an interval stated on the resistance. The location of this lever on the resistor strip will determine the value of the resistor.

In addition, the resistance also has a roller: used with nichrome wire material with high insulation and is often used in high -capacity applications, so absolute accuracy is needed. However, the drawback is that the resolution of this fuel is not really good.

Materials with impedance are the main raw materials commonly used to create disadvantages such as:

Carbon (coal variable): This is a common material made from carbon particles at a cheap cost, which is produced in large quantities, leading to high accuracy, so manufacturers have come to other alternative ingredients.

Rolls: This type of insulating wire is rolled with a high -powered nichrome wire suitable for high -power applications that need accuracy as well as longevity. However, its limitation is that the resolution is not good.

Electrical conductive resin: used for high -end audio applications with high price and only used in low -power applications.

Cermet: is a stable material, has a large heat resistance but the life expectancy is not high and the price is very expensive.

On the resistance will also have an adjustable knob to help us customize each resistance level suitable for the device and use requirements.

Principle of operation of resistance

The main operating principle of the resistance is that the conductors are separated and have different short lengths. They have microchips or control knobs. When controlling the knobs of the circuits, the length of the conductor will lead to the resistance in the circuit changes.

The electronic circuit design still has an error, so when adjusting the microchips, people must use resistance. At this time, the variable resistance has the role of voltage, the flow in the circuit.

For example, the sound increasing machine often uses resistance to change the volume.

Classification of resistance

Each type of resistance will have a different resistance value. They depend on the position of the extreme running on the resistance range. That’s why we can adjust the resistance value to control the voltage as well as the current.

In order to do so, there will be a fixed resistance range in the resistor between the two poles of the resistor and the third polar will move mobile on that resistor. In which, the length of the material will be proportional to the impedance. Therefore, when we change the position of the third pole on the resistor, it also means that the length of the material will also change and thereby change the value of the resistance.

Currently, the variable is divided into 4 main categories

• Turn back and hand

This type of resistance is called the turning back turner because it revolves around the coil. This type of resistance has almost the same components as the run. Instead of sliding along the coil like a run, in this type of variable will turn around the coil so the coil must also be designed in a circular shape instead of a cylindrical.

• Running back variable

It is called the ran -running variable because it has a structure of a slide along the coil.

The structure of this resistance consists of a long cylindrical core made of porcelain, wrapped around a metal string (made of nickel or Nicrom) with a large resistance and one runs. When the child slides along the coil, it will change the number of rings of the conductor, which leads to the value of the resistance also changes.

• Coal transformer (pressure extract)

This is the most common type of variable. This type of resistance has the core made of coal. So it is called coal resistance (resistance resistance). Regarding the principle of operation, it works like the type of turning back. Meaning also consists of a child running around a coal shaft wrapped in a conductor.

• Red wire variable

Designed to operate in the circuit containing DC current (DC) and two -way current (AC).

Application of the resistance in life

In fact, in everyday life, there are many applications of variables. A few common applications can be mentioned as:

• Volume variable

You may encounter this resistance in the volume twisting buttons of speakers, TV control, … When we adjust the switch, the sound will increase or decrease according to the requirements of use.

• Power resistance

Just like other common types of resistance but instead of having an Ohm resistor, the unit of this type of resistance is W.

The application of this power variable line is used to increase or decrease the capacity of the engine. (For example, if you want to increase or decrease the speed of the engine, use this resistance.)

• Thermal

The purpose of using this resistance is to increase or decrease the temperature simply. The application that you can see most is the temperature adjustment in hot water bottles used in the family.

• The resistance adjusts the brightness of the lamp

Just like a different variable Volume, this variable is used to increase or decrease the brightness of the light bulb.

In addition, in industry, the resistance is used to raise/lower the pistons of the bending or steel rolling system or can be used in analog line transmitters.

See also: The entire theory of the law of hugging (Ohm) and practice exercises

Solve some physical transformer exercises 9

To help reinforce the knowledge you have just learned, the following are exercises related to variables.

Lesson 1: Let the circuit have a diagram as shown

In which, the voltage between A and B is unchanged and the light lights normally when the resistance has a resistance with zero. Which of the following is the correct statement?

A. The light is strong when moving the run of the turn to the head m

B. Lights weaken when moving the run of the turn back to the head m

C. The light is strong when moving the run of the turn to the head n

D. All three sentences above are not correct

Solution instructions:

Answer A. The lights are strong when moving the run to the beginning of M.

Because the current has the direction from the anode (+) through the wire and the equipment and the negative cathode (-), at the end of M, when the child has not changed the length of the length has not changed, the resistance is the smallest, so the light is the brightest.

The run will run towards the point M, causing the length to decrease, so the resistance decreases. But the lights connected to the transformer will decrease the whole circuit, so the amperage increases, resulting in a strong light when moving the running of the turn to the head of M.

Lesson 2: A light bulb has a rated voltage of 2.5 V and a rated current of 0.4 A is connected to a ran -running variable for use with a constant voltage 12V

A. How to get together to get together so that the lamp can light up normally? Draw this circuit diagram

B. For normal lighting, how much resistance must be adjusted?

C. If the maximum resistance is 40 Ω, when the light light normally the current flows through the total number of rings?

Solution instructions:

A. Normal lights are Udh = UĐm = 2.5 V <U = 12 V

Therefore, there must be a light bulb and variable. The circuit diagram as shown below:

B. Normal lights, I = ID ĐM = 0.4 A

The resistance of the lamp is: Rđ = Uđ: Id = 2.5: 0.4 = 6.25 Ω

The whole circuit resistance is: RTĐ = U: I = 12: 0.4 = 30 Ω

Then the resistance has a resistance: Rb = RTĐ – RĐ = 30 – 6.25 = 23.75 Ω

C. Because the resistance of the resistor is proportional to the number of changes the rings when the lights are normal, the percentage (%) of the wire ring of the resistor has the current:

(23.75: 40) .100 % = 59,375 %

Lesson 3: A light bulb has a rated voltage of 3V and when the normal light is released, the current through the light has a intensity of 0.32A. This light bulb is connected to the variable and then the voltage is constant 12V. Asking this variable must have the maximum value at least so much for the lights to light up normally?

Solution instructions:

Because the light bulb is connected to the variable to make the light normally light, the amperage through the circuit must be equal to:

I = ID ĐM = 0.32 A and Uđ = Uđ ĐM = 3 V

The resistance is equivalent to the whole circuit:

RTĐ = U: I = 12: 0.32 = 37.5 Ω

Resistance of the light bulb: Rđ = Uđ: Id = 3: 0.32 = 9,375 Ω

The maximum resistance of the resistance:

RB = RTĐ – Rđ = 37.5 – 9,375 = 28,125 Ω

Conclude

Hopefully, with the knowledge as well as the exercises on Mầm non Cát Linh help you visualize and understand the knowledge related to the variable. Please often access the basic knowledge to be able to update yourself with useful lessons. Mầm non Cát Linh is very pleased to accompany you in the learning journey ahead.

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