Resistance, Reactance and Impedance (2330)

What is reactance?

When a coil of wire or a capacitor are connected to an AC supply the alternating (moving) current activates the reactive component of the coil or capacitor which creates extra 'resistance' to current flow.

What is the capacitive reactance of a 70 microfarad capacitor when connected to a 50Hz supply?

XC = 1 / 2 x 3.142 x 50 x (70 x10-6) = 45.47 ohms

What is the inductive reactance of a coil of 0.1H when connected to a 50hz supply?

XL = 2 x 3.142 x 50 x 0.1 = 31.42 ohms

How do you calculate impedance if you know the resistance and reactance of a circuit?

Because R and X are at 90 degrees to each other, when we add the third side Z we have formed a right angle triangle. So to calculate Z we can use Pythagoras.

What is the reactance caused by a capacitor called?

Capacitive Reactance (XC)

What is the total opposition to current flow called in an AC circuit?

Impedance (Z)

As well as opposing current flow, what other effect does reactance have on current?

It forces the current 90 degrees 'out of phase' with the voltage. R = resistance X = reactance Z = impedance

What is the difference between resistance and impedance?

Reactance (X) because: Resistance (R) + Reactance (X) = Impedance (Z)

What is the formula for calculating capacitive reactance?

F = frequency of the supply in Hertz (Hz) C = capacitance in farads (F)

What is the formula for calculating inductive reactance?

F = frequency of the supply in Hertz (Hz) L = inductance of the coil in Henry's (H)

What is the reactance caused by a coil of wire called?

Inductive Reactance (XL)

What is the formula for Pythagoras?

Or using our 'impedance triangle' we can substitute a, b and c for R, X and Z

What is the total opposition to current flow called in a DC circuit?

Resistance (R)

What is the formula for calculating impedance?

XL is replaced with XC if it is capacitive reactance in the circuit.

In a circuit with capacitive reactance the current 'leads' the voltage by 90 degress. True or False?

True

In a circuit with inductive reactance the current 'lags' behind the voltage by 90 degress. True or False?

True

What is the formula for calculating impedance in a circuit that contains both inductive and capacitive reactance?

XL and XC can be either way around. Just subtract whichever is smallest from whichever is largest