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