Experiment No. 5 Capacitor

The Capacitor

Function of Capacitor:

Capacitors store electric charge. They are used with resistor and timing circuits because it takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of charge. They are also used in filter circuits, because capacitors easily pass AC charging signal and block DC constant signal.

Capacitance

This is a measure of capacitors ability to store charge. A large capacitance mean that more charge can be stored. Capacitance is measured in farads symbol (F). However 1F is very large, so pre fixes are used to show the smaller values.

m Means 10 Power –6 (Millionth) so 1000000 m F = 1F

n Means 10 Power -9 ( Thousand Millionth)  1000nF = 1m F

P Means 10 Power -12 (Million-Millionth) 1000PF = 1nF

Identifying Capacitors "Size"

The following table can be used to figure out the capacitance if the Farad "size" is not printed on the capacitor and EIA code might be listed on the capacitor.

mF	nF	pF	EIA Code
0.00001*	0.01	10	100
0.0001*	0.01	10	101
0.001	1.0 (1n0)	1,000	102
0.01	10	10,000*	103
1.0	1000*	100,000*	104
1.0	1000*	1,000,00*	105
10.0	10,000*	10,000,00*	106

RC Time Delay or “Charging Time”

R * C * 5 = T

Capacitor Charging Circuit

Components: 1 x resistor, 1 x capacitor, 1 x pushbutton N/O switch.

Exercise: Calculate how much time would capacitor take to charge up following by connecting the circuit shown in the figure above. Measure time taken by the capacitor reaching the applied voltage on an oscilloscope.

Circuit number	Capacitance (uF)	Resistance (K W)	Calculated Time (ms)	Observed Time (ms)
1	100	1	500ms	470
2	100	0.1	50ms	50
3	100	0.47	230ms	240
4	330	1	1650ms	1600

How does changes in the resistor affect the charging time?

The initial charge is fast, however overtime the charging process is showing down as it charges and it almost gets to zero which means there is no capacitor for further charge.

How does charges in the capacitor affect the charging time?

The larger the capacitor is the longer it will take to charge and there would be less resistance in the circuit which will make the capacitor to charge faster.