Resistance is short for resistor. What the questioner said is that the resistance is large, which can be understood as two kinds: the resistance value of the resistance is large and the volume of the resistance is large.
There are many kinds of resistors, such as carbon film resistance, metal film resistance, metal oxide film resistance, glass glaze resistance, synthetic carbon film resistance, wire wound resistance, patch resistance and so on.
Resistance value is not directly related to power. For example, carbon film resistance belongs to thin film resistance. It is formed by depositing resistance film on carbon rod substrates. The thickness of this resistance film is less than several microns, so it is impossible to make a large power for this type of carbon film resistance. Generally, it can achieve 1/16W. 1/8W, 1/4W, 1/2W, 1W, 2W. But their resistance range can be very wide from 0.5_to 10_6_.
The resistance of metal film is larger than that of carbon film (10 x 10_7_). The resistance of metal oxide film is narrower, and the general resistance is less than 200 K_. The resistance of synthetic film can range from 10_to 10_6 M.
Wire-wound resistors or cement resistors are required to achieve high power.
- (1) Wire winding resistance is made by winding the ceramic tube with constantan wire or nickel-chromium alloy and coating the outer layer with enamel or glaze protective layer. Its maximum power can reach 200W.
- (2) Cement resistance is made by winding a glass fiber column with a resistance wire of lower resistance ratio and encapsulating it with a ceramic shell. These resistors are classified into RX27-1, RX27-1V, RX27-3 (A, B, C), RX27-4 and so on. The power range of RX27-1 is 2-15W, the resistance range is 0.1-2200; the power range of RX27-3 is 5-15W, the resistance range is 0.1-2700; and the power range of RX27-4 is 10-40W, and the resistance range is 0.1-4300.
Simply from the volume of resistance, the larger the volume, the greater the power in it. Because resistance emits a lot of heat and consumes power when it passes through with current, resistor manufacturers make calculations based on its rated resistance and power. Otherwise, it will appear that the resistor is hot, scorched or even burned out.
In view of the above situation, the concepts of heat-resistant power, rated power and nominal power of resistors are introduced. Heat-resistant power refers to the amount of heat dissipation that a resistor can withstand per unit time, in terms of watt (W). Usually, the heat dissipation of resistors is related to the heat dissipation conditions; the larger the volume of resistors, the easier the heat dissipation, so the larger the volume of the same type of resistors, the greater the heat resistance power. Rated power refers to the maximum power allowed to be consumed by a resistor for a long time, and its calculation formula is: P=IU P=I_R P=U_/R is the rated power of the resistor, unit W; I is the current flowing through the resistor, unit ampere (A); U is the voltage at both ends of the resistor, unit V; R is the resistance value of the resistor, unit Omega.