Transcript Capacitor

Capacitors
Charge is forced
on to primary
plate by voltage
C=
Charge is repelled off
of secondary plate
creating voltage
Q
V
V
Charging
A
p.d. across
capacitor
R
Discharging
A
p.d. across
capacitor
R
mA
mA
Set up this circuit and observe the current flow.
Describe it as fully as you can.
What should you have observed?
• Current starts high and ends low (0)
• Current reduces rapidly to begin with
• Current reduces more slowly as time goes on
So…
Current discharge from a capacitor is
Exponential
R
V
mA
C
mA
Use a voltmeter to investigate the relationship
between R or C and the ‘half life’ of the voltage
1000 MicroF - 15k
1000 MicroF - 6k6Ohms
1000 MicroF - 3k3Ohms
5.00
p.d. (Volts)
3.75
2.50
1.25
0.00
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Tim e (Sec)
35.0
40.0
45.0
50.0
55.0
60.0