Given this, we can say that these three quantities– power, voltage and current, are in a power triangle. In other words, if resistance is subjected to a voltage, or if it conducts a current, then it will always consume electrical power. In Ohm’s law, when a current flows through a resistance, a voltage is dropped across it producing a product that relates to power. Resistor Power Rating is defined as the amount of heat a resistor can handle without sacrificing its performance in no definite time. A resistor can be functional at any combination of voltage and current as long as it does not exceed the power rating that a resistor can convert into heat or absorb without any damage. The greater the current flow, the hotter the resistor will be. Resistor Power RatingĮverytime a current passes through a resistor due to the presence of a voltage across, electrical energy is lost in the form of heat. For example, 0R5 would be 0.5Ω, and 0R01 would be 0.01Ω. Note: The letter “R” is used to indicate the position of a decimal point for resistance values lower than 10 ohms. In this system, the first two or three digits indicate the numerical resistance value of the resistor, and the last digit gives a multiplier– the power of ten by which to multiply the given resistor value. Table of Values for EIA-96 System Three- and Four-Digit System Resistivity varies for different materials. Silicon has a resistivity of about 1000 Ωm and glass measures about 1012 Ω-m. At room temperature, aluminum comes in at about 2.8 x 10 -8 -Ωm, while copper is significantly lower at 1.7 x 10 -8 Ω-m. Note: Conductors have much lower resistivity than insulators. Having said that, Georg Ohm came up with an equation that explains this relationship: where ρ = resistivity (Ω-m) On the other hand, resistance decreases as the thickness of wires increases. This means that the longer and thinner wires offer more resistance. He proved that the resistance (R) of a material increases as its length increases. George Ohm studied the relationship between resistance and the size of the material that was used to make the resistor. As we’ve found out, it’s easier for the electrons to flow in some conductor materials than insulators. The thinner the copper, the higher the resistance since it’s harder for the electrons to pass through it. Resistance depends on those copper turns. However, if you break it open, you’ll see an insulating ceramic rod running through the middle with copper wire wrapped around the outside. If you look at resistors from the outside, they most likely look the same. Wiring a resistor in a circuit will reduce the current by a precise amount. Examples of this are potentiometers, rheostats, trimmers, and so on. The slider taps onto the main resistor element so there will be three connections two are connected to the third element and one to the slider. Variable resistors have fixed resistor elements plus a slider. It can also be made with a mixture of finely ground carbon or be very small in size and for high power rating. It can have a carbon composition or chip-and-wire wound type. Their values should never be changed to adjust the circuit since those were determined during the design phase. Fixed resistors are designed to set the right conditions in a circuit.
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