# Capacitors

## Capacitors - National 5 Recap

### A Capacitor is a device for storing Electrical Charge. A Capacitor consists of two parallel plates separated by an insulator. The symbol for a Capacitor is shown below:- ## Capacitors in Circuits

### The diagram below shows a simple Capacitor circuit:- ## Capacitor Graphs

### As the Voltage across the Capacitor increases, the Potential difference between the battery and Capacitor gets smaller, so the Current decreases. This causes the curved shape of the following Voltage and Current graphs of a charging and discharging Capacitor:- ## 'Filling' a Capacitor

### The graphs below show the effect on the Current flow due to Capacitance and Resistance:- ## Numerical Calculations - Charge and Voltage

### By measuring the Charge built up on a Capacitor as the Voltage of the supply is increased, the following graph can be generated:- ## Numerical Calculations - Energy Stored

### The total Energy stored by the Capacitor can be found graphically, by finding the area under a Charge-Voltage graph:- ## Capacitor Case Study : Traffic Lights ### The diagram below shows the Transistor circuit that would allow this system to work:- 