reactance and impedance - Overview, Structure, Properties & Uses

Reactance and Impedance - Definition, Formula, FAQs

Edited By Team Careers360 | Updated on Jun 13, 2022 11:48 AM IST

Impedance:- impedance meaning (impedance meaning in English) hindrance. Impedance definition ( impedance definition physics ), “It is the combined opposition of the resistor, inductor and/or capacitor to flow of a.c. in the circuit”. Impedance is also known as electrical impedance.

Impedance symbol is the Z. The Impedance unit is the ohm, which is called the impedance because it impedes the flow of alternating current in the circuit. Impedance meaning in Hindi प्रतिबाधा. Impedance meaning in Tamil is மின் தடுப்பு

What is the formula for impedance? Let’s discuss it. The impedance formula or electrical impedance formula in the different circuits is different.

Key points:-

Impedance, impedance meaning, what is impedance (or what is electrical impedance), impedance formula, impedance unit.
Reactance, what is reactance, reactance formula, reactance unit, reactance meaning etc.,
What is admittance, admittance formula, XC meaning.

Also read -

Impedance formula in L-R series circuit:-

i = V/√(R² + X²L)

Applying Ohm's law, we see that √(R² + X²L) is the effective resistance of the circuit. It is called the impedance of the circuit, which is represented by Z. Thus in L - R circuit, we have

Z = √(R² + X²L)

Where R and XL are resistance and inductive reactance.

But XL = ⍵L.

Z = √(R² +(⍵L)²)

As a resistance, impedance also has a unit, and what is the unit of impedance. The answer is the SI unit of impedance is ‘ohm’.

But a term derived from impedance is admittance. So, what is the admittance? We can define admittance as, “The reciprocal of impedance is called ‘admittance’.” Unit of impedance is ‘mho’ or ‘ohm-¹’ (Ω-¹) or ‘siemen’ (S). Admittance formula is

Y = 1/Z

Impedance and admittance both are reciprocal to each other.

Related Topics,

The impedance of R - C series circuit;-

i = V/√(R² + X²C)

Similarly, Z = √(R² + X²c)

Where R and Xc are resistance and capacitive reactance.

But Xc = 1/⍵C.

∴ Z = √(R² + (1/⍵C)²)

Impedance formula of R-L-C series circuit:-

i = V/√ (R² + (X_L- X_c)²)

Similarly, Z = √ (R² + (X_L - X_c)²)

But XL = ⍵L and Xc = 1/⍵C

∴ Z = √ (R² + ( ⍵L- 1/⍵C )²)

Impedance triangle:- What is impedance triangle? The impedance of an L-C-R circuit is given as

Z = √ (R² + (XL - Xc)²)

And the phase relationship is given by

tan? = XL - Xc/R

In terms of the resistance and the reactances of the circuit, elements may be expressed by means of a right-angled triangle, as shown in fig. This triangle is called an impedance triangle.

right-angled triangle

The impedance of capacitor:- It impedes the flow of current in the capacitor.

The capacitor impedance formula is

Impedance of inductor:- It impedes the flow of current in the inductor. It measures the resistance of the current in the inductor.

Inductor impedance formula is

ZC = jL⍵

Reactance:- What is reactance? We can define reactance as, “The reactance is the opposition offered by an inductor or by a capacitor or by both.” So it is the reactance definition.

Reactance meaning in hindi विरोध. The unit of reactance is ‘ohm’. The reactance symbol is ‘X’

Reactance formula:- The formula of reactance is

X = XL + Xc

Where XL and XC are inductive reactance and capacitive reactance respectively.

Later, we also discuss the XL and Xc formula.

NCERT Physics Notes:

Inductive resistance:-The peak value of current in the coil is

i0 = V0/⍵L

Applying Ohm's law, we find that the product ωL has the dimension of resistance. It represents the effective opposition of the coil to the flow of alternating current. It is known as ‘inductive resistance’. It is denoted by XL.

XL = ωL = 2πfL

Where f is the frequency of the alternating current. Thus, the inductive reactance increases with increasing frequency of the current (XL ∝ f). The graph between XL and f is, therefore, a straight line.

Where L is in henry and f in hertz (cycle/second), then the XL (= 2πfL) inductive reactance unit (or SI unit of reactance )is ohm. The inductive reactance XL is zero for d.c. for which f = 0.

Capacitive reactance:- The peak value of current in the capacitor circuit is

i0 = V0/1/⍵C.

Applying Ohm’s law, we find that the quantity 1/ωC has the dimensions of resistance. It is the effective opposition of the capacitor to the flow of alternating currents. It is known as the reactance of the capacitor or capacitive inductance and is denoted by XC. So, Xc meaning is capacitive reactance.

Xc = 1/ωC = 1/2πfC

Where f is the frequency of the alternating current. Thus, the capacitive reactance decreases with the increasing frequency of current (Xc ∝ 1/f). The graph between the Xc and f, is, therefore, a rectangular hyperbola.

When C is farad and f is in hertz then Xc is in ohm. The capacitive reactance is infinite for d.c. for which f = 0.

The reciprocal of reactance is called ‘susceptance’ of the a.c. circuit. Unit of susceptance is ‘mho’ or ‘ohm-¹’ (Ω-¹) or ‘siemen’ (S). Susceptance meaning in hindi ग्रहणशीलता

Power

Also read :

Reluctance:- Reluctance is like resistance in a magnetic field, it opposes the magnetic flux in the field. The reluctance symbol is S

S = l/μ0μrA

In above we discuss reactance and impedance, and we clearly understand what is reactance and impedance?

Power factor of an alternating-current circuit:- When an alternating current circuit contains, besides resistance, inductance or capacitance or both, then the average power dissipation in the circuit is Vrms ☓ irms ☓ cosϕ when is phase difference between voltage and current. The factor is called power factor where cosϕ

There is a 5 Ω resistance in an AC circuit. Inductance of 0.1 H is connected with it in series. If equation of AC e.m.f is 5 sin 50t then the phase difference between current and e.m.f is:

Solution:- R = 5Ω,

L = 0.1 H

ω = 50

We know that, cosφ = R/Z = R/√(R² +(⍵L)²) = 5/√{(5)² + (50 ✖ 0.1)²}

Cosφ = 5/ √{25 + 25} = 5/√50 = 5/5√2 = 1/√2

Cosφ = cos 45°

Φ = ?/4

Power factor of the following circuit will be zero

Inductor
Capacitor
Conductor and inductor
Resistor

Ans: Option (iii) is correct

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Frequently Asked Question (FAQs)

1. What is meant by impedance? Or what is impedance in physics?

It is the combined opposition of the resistor, inductor and/or capacitor to flow of a.c. in the circuit.

2. Difference between impedance and reactance.

Impedance:- It is the combined opposition of the resistor, inductor and/or capacitor to flow of a.c. in the circuit.

Reactance:-The reactance is the opposition offered by an inductor or by a capacitor or by both.

3. Distinguish between resistance and reactance.

Resistance:-The resistance is the opposition offered by a resistor to the flow of a.c. in a circuit.

Reactance:- The reactance is the opposition offered by an inductor or by a capacitor or by both.

4. Write down the expression for the impedance of an R-C circuit

Z = √(R² + (1/⍵C)²)

5. The resistance of a coil for direct current is 5Ω. What will be the effect on its resistance when connected in the alternating current circuit?

The resistance will increase. The effective resistance (impedance) for a.c. will be √(R² +(⍵L)²).