## Main Difference – Resistance vs. Reactance

Resistance and Reactance are properties of an electrical circuit that opposes current. The **main difference** between resistance and reactance is that **resistance measures the opposition to a flow of current**, whereas **reactance measures the opposition to a change in current**.

## What is Resistance

The **resistance** () of a component in a circuit is the potential difference () across the component divided by the current () through the component:

If a resistor is added to a circuit powered by an alternating current, the changes in current will occur simultaneously with changes in voltage.

## What is Reactance

**Reactance** is an opposition to a *change* in current. Reactance is a property of capacitors or inductors because their functionality is intimately related to the *rates of change* of current and voltage.

## Capacitive Reactance

When a capacitor is connected to a circuit with an alternating power supply, the voltage across the capacitor and the current through the capacitor does not change simultaneously. The potential difference across the capacitor is changing in response to the alternating power supply. The rate at which charges accumulate/leave the plates is greater when the potential difference is changing at a faster rate. Consequently, the current is at a maximum when the potential difference is around 0 (this is when the *rate* of change of potential difference is highest). The graph below illustrates how the current and potential difference changes. We say that the current *leads* potential difference by a quarter-cycle (the maximum voltage comes quarter-a-cycle *after* the current):

The maximum potential difference across the capacitor, is given in terms of the maximum current in the circuit and the **capacitive reactance** of the capacitor, , as . For a capacitor with capacitance connected to a circuit whose alternating current has a frequency , the capacitive reactance is given by:

## Inductive Reactance

When the current across an inductor changes, a potential difference develops across it. The potential difference is proportional to the rate of change of current. Consequently, for inductors potential difference *leads* the current by a quarter cycle.

The potential difference across the inductor is given gy , where is the maximum current and is the **inductive reactance**. If the inductance of the inductor is and the frequency of the alternating current is , then:

Note that capacitive and inductive reactance can both be described as a ratio of potential difference to current. As a result, both types of reactances have units of ohms (Ω).

## Difference Between Resistance and Reactance

### Variation of Current

**Resistance** is a property of a component that opposes a flow of current.

**Reactance** is a property of a component that opposes a *change* in current.

### Power Dissipation

**Resistance** leads to a dissipation of power.

**Reactance** does not lead to power dissipation (for ideal capacitors and inductors).