Impedance vs resistance
1 Answer
Impedance and resistance are two related but distinct concepts used in the study of electrical circuits. They both represent opposition to the flow of electrical current, but they have different characteristics and are used in different contexts.
1. Resistance:
Resistance (denoted by the symbol "R") is a fundamental property of an electrical component or material that describes its opposition to the flow of direct current (DC). It is a scalar quantity, measured in ohms (Ω). When a voltage is applied across a resistor, a current flows through it according to Ohm's law: V = I * R, where V is the voltage, I is the current, and R is the resistance.
The resistance of a component remains constant regardless of the frequency of the AC (alternating current) signal passing through it. For example, in a purely resistive circuit, like a simple lightbulb or a resistor, the voltage and current are in phase with each other.
2. Impedance:
Impedance (denoted by the symbol "Z") is a more general concept that encompasses resistance but also includes reactance. Impedance is used to describe the opposition to both direct current (DC) and alternating current (AC) in electrical circuits. It is a complex quantity, meaning it has both magnitude and phase angle.
Impedance includes two components: resistance (R) and reactance (X). Reactance is a measure of the opposition to AC caused by capacitance or inductance in a circuit. The total impedance (Z) of a component or circuit is given by the formula: Z = √(R^2 + X^2), where R is the resistance and X is the reactance.
In AC circuits, impedance takes into account the phase relationship between voltage and current. In capacitive circuits, the current leads the voltage, leading to a negative reactance (inductive reactance), while in inductive circuits, the current lags the voltage, leading to a positive reactance (capacitive reactance).
To summarize, the key differences between impedance and resistance are:
- Resistance is a scalar quantity that represents opposition to direct current (DC) flow.
- Impedance is a complex quantity that represents opposition to both DC and alternating current (AC) flow and includes both resistance and reactance components.
- Resistance remains constant with frequency, while impedance can vary depending on the frequency and phase angle of the AC signal.
1. Resistance:
Resistance (denoted by the symbol "R") is a fundamental property of an electrical component or material that describes its opposition to the flow of direct current (DC). It is a scalar quantity, measured in ohms (Ω). When a voltage is applied across a resistor, a current flows through it according to Ohm's law: V = I * R, where V is the voltage, I is the current, and R is the resistance.
The resistance of a component remains constant regardless of the frequency of the AC (alternating current) signal passing through it. For example, in a purely resistive circuit, like a simple lightbulb or a resistor, the voltage and current are in phase with each other.
2. Impedance:
Impedance (denoted by the symbol "Z") is a more general concept that encompasses resistance but also includes reactance. Impedance is used to describe the opposition to both direct current (DC) and alternating current (AC) in electrical circuits. It is a complex quantity, meaning it has both magnitude and phase angle.
Impedance includes two components: resistance (R) and reactance (X). Reactance is a measure of the opposition to AC caused by capacitance or inductance in a circuit. The total impedance (Z) of a component or circuit is given by the formula: Z = √(R^2 + X^2), where R is the resistance and X is the reactance.
In AC circuits, impedance takes into account the phase relationship between voltage and current. In capacitive circuits, the current leads the voltage, leading to a negative reactance (inductive reactance), while in inductive circuits, the current lags the voltage, leading to a positive reactance (capacitive reactance).
To summarize, the key differences between impedance and resistance are:
- Resistance is a scalar quantity that represents opposition to direct current (DC) flow.
- Impedance is a complex quantity that represents opposition to both DC and alternating current (AC) flow and includes both resistance and reactance components.
- Resistance remains constant with frequency, while impedance can vary depending on the frequency and phase angle of the AC signal.