# Difference Between Resistance And Impedance

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## What Is Electrical Resistance?

Electrical resistance is the hindrance to the flow of charge through an electric circuit. Resistance is represented by the uppercase letter R. The standard unit of resistance is the ohm, sometimes written as a word and sometimes symbolized by the uppercase Greek letter omega.

In general, when the applied voltage is held constant, the current in a direct-current (DC) electrical circuit is inversely proportional to the resistance. If the resistance is doubled, the current is cut in half, if the resistance is halved, the current is doubled. This rule also holds true for most low-frequency alternating-current (AC) systems, such as household utility circuits.

The resistance of an object depends in large part on the material it is made of. Objects made of electrical insulators like rubber tend to have very high resistance and low conductivity, while objects made of electrical conductors like metals tend to have very low resistance and high conductivity. The nature of material is not the only factor in resistance and conductance; however, it also depends on the size and shape of an object.

### What You Need To know About Resistance

• Resistance can be described as the hindrance to the flow of charge in an electric circuit whether AC or DC.
• The value of resistance is independent of supply frequency.
• Resistance occurs in both AC and DC circuit.
• Resistance is the contribution of the resistive element in the circuit.
• Resistance consists of only real numbers. Example 4.4 ohms, 6.8 ohms, 7.4 ohms.
• Resistance if kept in an electromagnetic field represents power dissipation in any material.
• Resistance is denoted by symbol ( R).
• Resistance does not have a magnitude and phase angle.

## What Is Impedance?

Electrical impedance is the measure of the opposition that a circuit presents to current when a voltage is applied. Impedance is a more general term for resistance to an alternating current (AC) that also includes reactance. What is meant by this is that impedance includes both resistance (opposition of the electric current that causes heat) and reactance (the measure of such an opposition to AC electricity due to capacitance or inductance). In the direct current (DC), electrical impedance is the same as resistance, except that it does not hold true in AC circuits.

Impedance can also be different from resistance when an AC circuit changes flow in one manner or another, like the opening and closing of an electrical switch, as is observed in computers when they open and close switches to represent ones and zeros (binary language). The opposition of impedance is admittance, which is the measure of the allowance of current.

### What You Need To Know About Impedance

• Electrical impedance is the measure of the opposition that a circuit presents to current when a voltage is applied.
• The value of impedance depends on the supply frequency.
• Impedance takes place only in an AC circuit.
• Contribution of both resistance and reactance forms impedance.
• Impedance consists of both real and imaginary numbers. Example: R+id, where R is a real number and id is an imaginary part.
• If impedance is subjected to magnetic field it represents both power dissipation and energy.
• Impedance is denoted by symbol (Z).
• Impedance has a phase angle and magnitude.

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