There are fundamental differences between components and devices, such as resistors, capacitors and inductors, which do not change the internal molecular structure in production, that is, the performance only depends on the material. Devices generally refer to semiconductors, such as diodes, transistors, etc., whose molecular structure is altered during production. For example, in the production of the transistor, the concentration of most carriers in the emission region is higher than the base region, which changes the molecular structure, so it is a device. Below according to the question to say the role of a few kinds of components.

The role of resistance: resistance is widely used in the circuit, there are several functions, such as shunt, partial voltage, current limit. The resistors are shunt in parallel, and the voltage is divided in series. As for current limiting, the leds we use usually have a resistor in series. The function of this resistor is current limiting, so as to avoid excessive current burning the leds, as shown in the figure below.

The role of capacitance: the role of capacitance is more, there are filtering, bypass, coupling, energy storage and so on. One of the things that we see and use a lot on the circuit board is the filtering function, whenever it’s a power supply circuit, it’s capacitive filtering. No matter what the role, it is the use of capacitor-separated straight – through intersection, the characteristics of high resistance. The following figure shows a power supply circuit with capacitive filtering.

The role of inductance: inductance in the circuit is not used as much as resistance and capacitance, the main role is filtering, oscillation, delay, notch, etc., no matter what the role, is to make use of the inductance through the cross, through the characteristics of low resistance and high capacitance, and the opposite. The following figure shows an LC filter circuit composed of inductance and capacitance.