# Capacitors/inductors have memory?

1. Aug 25, 2014

### dgamma3

Hello, my textbook states that "Circuits that contain capacitors and/or inductors have memory". In what sense do they have memory?
my understanding of memory, is retaining value. how do inductors/capacitors retain value?

thanks
daniel

2. Aug 25, 2014

### jaydnul

An inductor stores energy in its magnetic field, a capacitor stores energy in its electric field. "Memory" might just be a poor choice of words although I'd guess you could extract some information about the circuit from the amount of energy stored at a given moment.

3. Aug 27, 2014

### Born2bwire

A capacitor can retain memory of a voltage and an inductor a memory of a current in a sense. For example, an integrator can be built using an opamp and a capacitor. The capacitor acts as a memory of the integral and holds the output voltage when the input goes to null. The integtal is obtained by building up the voltage across the cap. You have to have a reset circuit to drain the cap to start the integration afresh. An inductor could do something similar for a current as it strives to maintain a current through it but it is not as effective due to an inductor's resistive losses draining the current. But this idea of memory should be cautiously applied to certain situations.

4. Aug 27, 2014

### CWatters

The voltage drop across a resistor at any instant in time depends on the current at that time. The voltage drop across a capacitor at any instant in time depends on the charge (aka current) that flowed into it in the past. Memory is a reasonable word to describe a parameter that depend on past data.