Basic symbol of resistance

There are two international standards for fixed resistors. The common ones are shown in Figure 1 and Figure 2. The former is adopted as a national standard, while the latter is common abroad.

Early resistors were composed of ceramic cylinders and two lead wires. The main body of the resistor was mostly made of ceramic, with a carbon film on the surface. The resistance was adjusted by cutting the ring. High-power resistors were wound with alloy wires. For high-power resistors, metal films were used, but the cost was relatively high.