The document discusses capacitors, including their construction using two conductive plates separated by an insulating material, how they store electric charge, and definitions of capacitance and factors that determine it such as plate size and separation distance. It also covers graphical representations of capacitors, how energy is stored in capacitors, the exponential charging and discharging behavior over time defined by the time constant, and using logarithmic graphs to determine the time constant.

1. Capacitors

2. What is a capacitor? Electronic component Two conducting surfaces separated by an insulating material Stores charge Uses Time delays Filters Tuned circuits

3. Capacitor construction Two metal plates Separated by insulating material ‘ Sandwich’ construction ‘ Swiss roll’ structure Capacitance set by...

4. Defining capacitance ‘ Good’ capacitors store a lot of charge… … when only a small voltage is applied Capacitance is charge stored per volt Capacitance is measured in farads F Big unit so nF, mF and  F are used

5. Graphical representation Equating to the equation of a straight line Gradient term is the capacitance of the capacitor Charge stored is directly proportional to the applied voltage Q V

6. Energy stored by a capacitor By general definition E=QV product of charge and voltage By graphical consideration... Area term is the energy stored in the capacitor Q V

7. Other expressions for energy By substitution of Q=CV

8. Charging a capacitor Current flow Initially High Finally Zero Exponential model Charging factors Capacitance Resistance I t

9. Discharging a capacitor Current flow Initially High Opposite to charging Finally Zero Exponential model Discharging factors Capacitance Resistance I t

10. Voltage and charge characteristics Charging Discharging V or Q t V or Q t

11. Product of Capacitance of the capacitor being charged Resistance of the charging circuit CR Symbol  ‘Tau’ Unit seconds Time constant

12. When t equals tau during discharge At t = tau the capacitor has fallen to 37% of its original value. By a similar analysis tau can be considered to be the time taken for the capacitor to reach 63% of full charge.

13. Graphical determination of tau V at 37% Q at 37% Compared to initial maximum discharge V or Q t

14. Logarithmic discharge analysis Mathematical consideration of discharge Exponential relationship Taking natural logs equates expression to ‘y=mx+c’ Gradient is -1/Tau

15. Logarithmic discharge graph Gradient term is the -1/Tau lnV t

16. www.search for... Capacitors