Resistance is a basic concept in electronics that describes the degree to which an electrical current is obstructed in a circuit. In DC circuits, resistance is a kind of resistance effect of a conductor on the current, and its magnitude is measured by the value of resistance, the unit is ohmic ( ) The basic formula for resistance is r=u i, where r represents the resistance value, u represents the voltage, and i represents the current. This means that when given a voltage and a resistor, the magnitude of the current is determined by the resistance of the resistor.
The resistance to the current is achieved by converting electrical energy into heat energy. When an electric current is passed through a resistor, there is a collision between the electrons inside the resistor and the atoms, resulting in an obstruction of the movement of the electrons. These collisions result in a loss of energy, which converts electrical energy into heat.
The development of resistors can be traced back to the early 19th century. The earliest resistors were invented in 1845 by the English physicist William Thomson (later known as Lord Kelvin). He used a resistor made of constantan wire, one of the first metal resistors. However, the concept of electrical resistance was proposed as early as the ancient Greek and Roman periods, when it was discovered that certain substances had the property of hindering the passage of electric current.
In the mid-19th century, with the rise of communication technologies such as the telegraph and **, the demand for resistors increased. Scientists began to systematically study the phenomenon of resistance and came up with Ohm's law, which states that current is proportional to voltage and inversely proportional to resistance. This discovery provides a theoretical basis for the manufacture and application of resistors.
Subsequently, various different types of resistors were introduced. In 1885, British scientist C. Bradley invented the molded carbon solid core resistor, which was an important breakthrough in resistor manufacturing technology. In 1897, British scientists T. Gambrill and A. Harris used carbon-containing ink to make carbon film resistors, which have better stability and reliability. At the beginning of the 20th century, metal film resistors and thermal decomposition carbon film resistors were also invented.
With the rapid development of electronic technology, the types and performance of resistors have also been continuously improved and enhanced. For example, since the 60s of the 20th century, resistors manufactured by new processes such as drum magnetron sputtering and laser resistance fine-tuning have higher precision, smaller volume and better stability. In addition, with the continuous emergence of new materials and technologies, the application fields of resistors are also expanding, involving various fields such as communications, computers, aerospace, and medical treatment.
There are many types of resistors, which can be divided into the following categories according to the material, structure, and use scenario:
Carbon Film Resistance:It is made with carbon as the main material and coated with carbon film on an insulating substrate. Carbon film resistors have the characteristics of low cost and good stability, and are widely used in various electronic devices.
Metal Film Resistance:It is made by evaporating a metal film on an insulating substrate using metal as the main material. Metal film resistors have the advantages of high precision, good stability, and low noise, and are often used in precision instruments and measuring equipment.
Winding Resistance:It is made by wrapping a metal wire around an insulator. Wirewound resistors have the characteristics of high temperature resistance and high voltage resistance, and are often used in high-power circuits.
Thermistor:Resistance with a change in resistance with temperature. Thermistors are often used for temperature sensing, temperature control, etc.
Photoresistors:Resistance that varies with the intensity of the light. Photoresistors are often used in photoswitching, photoelectric sensors, etc.
Resistance plays a vital role in the circuit, mainly including the following aspects:
Current throttling:By adjusting the resistance of the resistor, the current in the circuit can be limited and the circuit equipment can be protected from excessive current.
Partial pressure:Resistors can distribute the voltages in a circuit so that different parts of the circuit get the right voltage value.
Filtering:In some circuits, resistors can be combined with other components to act as filters to reduce noise and interference in the circuit.
Temperature Compensation:Special resistors, such as thermistors, can adjust the resistance value according to changes in temperature, and are used for temperature compensation and temperature detection of circuits.
When choosing a resistor, there are several aspects to consider:
Resistance:Select the appropriate resistance value according to the circuit requirements. Too much or too little resistance may affect the normal operation of the circuit.
Power:Make sure that the resistor you choose is able to withstand the power in the circuit. Resistors that are too low in power can be damaged by overheating.
Accuracy:For circuits that require precise control of voltage or current, a resistor with higher accuracy should be selected.
Working Environment:Consider the working environment of the resistor, such as temperature, humidity, etc. In harsh environments, the corresponding special resistors should be selected.
In addition, the following precautions should be taken when using resistors:
Follow safety norms:When installing and using resistors, the corresponding safety specifications should be followed to ensure the safety and stability of the circuit.
Prevent overheating:Avoid leaving the resistor at high temperature for a long time to prevent overheating damage.
Regular check-ups:Check the working status of the resistor regularly, and replace it in time if any abnormalities are found.
There are many types of resistors as basic components in electronic circuits, and each resistor has its own unique model and characteristics. Here's a quick rundown of some of the classic resistor models:
1 4W Carbon Film Resistor:This is one of the most common types of resistors and is commonly used in electronic circuits in general. Its resistance ranges from a few ohms to several megaohms. Due to its low cost and stable performance, it is widely used in various electronic devices.
1 2W Metal Film Resistor:This type of resistor is typically more accurate than a carbon film resistor and is suitable for circuits that require higher accuracy. It also has a wide range of resistance values, but the cost is relatively high. Metal film resistors are commonly used in precision instruments and measuring equipment.
1W Wound Resistance:This resistor is capable of withstanding large amounts of power and is typically used in high-power circuits. Due to its special structure, the resistance range is relatively small, but the stability and reliability are very high.
NTC (Negative Temperature Coefficient) Thermistor:The resistance of this resistance decreases as the temperature increases. It is often used in temperature detection and control systems, such as air conditioners, refrigerators, etc.
PTC (Positive Temperature Coefficient) Thermistor:In contrast to NTC, the resistance of this resistor increases with increasing temperature. It is commonly used in overcurrent protection and temperature control systems.
Photoresistor (LDR):The resistance of this resistor decreases as the intensity of the light increases. It is often used in light control switches, photoelectric sensors and other occasions, such as the control system of street lights, automatic doors and other equipment.
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