Capacitive ReactanceCapacitive Reactance
Capacitors in AC CircuitsCapacitors in AC Circuits
CapacitanceCapacitance
Capacitance also Capacitance also causes opposition to causes opposition to current flow.current flow.
Blocks DCBlocks DC.. V
I
V
I
CapacitanceCapacitanceThe farad (symbol: F) is the SI unit of The farad (symbol: F) is the SI unit of
capacitance. capacitance.
It is named after the British physicist It is named after the British physicist Michael Faraday.Michael Faraday.
Voltage
Current
Capacitor in DC
ICE
I C EI C ECurrentCurrent CapacitanceCapacitance VoltageVoltage
Current leads VoltageCurrent leads Voltage
in ain a
Capacitive CircuitCapacitive Circuit
Voltage
Current
Capacitor in AC
Voltage Current
V = Vpsin(2πft) Vp-Peak Voltage
2π-Cycle
f-frequency(Hz)
t-time(seconds)
I = C dv/dt
I = C Vp(2πf)cos(2πft)
Ip = Vp(2πf)C
Ip = Vp(2πf)C Ip = Vp/R
1/R = 2πfC
R = 1/(2πfC)
Capacitive Reactance
Xc = 1/(2πfC)
C is an Active Component
Capacitance in AC CircuitsCapacitance in AC Circuits
Capacitive ReactanceCapacitive Reactance
The opposition to current flow The opposition to current flow caused by a capacitor is known caused by a capacitor is known as capacitive reactance.as capacitive reactance.
Capacitive reactance, as it is Capacitive reactance, as it is opposition to current flow, is opposition to current flow, is measured in Ohms measured in Ohms Ω.Ω.
The symbol for capacitive The symbol for capacitive reactance is Xreactance is XC.C.
The formula is:The formula is:
fCXC 2
1
1mF = 1 X 101mF = 1 X 10-3-3FF
11μμF = 1 X 10F = 1 X 10-6-6FF
1nF = 1 X 101nF = 1 X 10-9-9FF
1pF = 1 X 101pF = 1 X 10-12-12FF
Capacitor Values
Find the current flowing in a circuit when a 4μF capacitor is connected across a 880v, 2000Hz power supply.
C = 4C = 4μμF = 4 X 10F = 4 X 10-6-6FF
Vp = 880VVp = 880V
f = 2000Hzf = 2000Hz
Find: IpFind: Ip
Xc = 1/(2πfC)
Xc = 1/(2π(2000Hz)(4x10-6F)
Ip = Vp/Xc
Ip = 880v/19.9Ω
Xc = 19.9Ω
Ip = 44.2A