How is resistor size, capacitor sizes....etc. determined in circuits?

110100101108 years ago
resistor reduces current. its size is detemined by the wanted current in the circuit. the wanted current is often determined by the max amount of heat allowed in the circuit so it won't get damaged capacitor stores energy. its size is determined by the amount of reserve enegy wanted. in some circuits (like 555) it acts like a sand clock - the time it takes for it to charge or discharge is used for timing something else. the time depends on size of capacitor. in dc power supplies it is used to smooth out voltage spikes. the size is determined by the largest expected spikes. in such circuits larger capacitor can be used as well and usually is better (can deal with larger spikes) capacitor filters ac frequencies. it can be used in stuff like equalizers for sound. the frequencies filtered and the depth of filtering depends on the size of capacitor capacitor can act as resistor on ac. then its size is determined using the same considerations as resistor