# Mr Electro

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## Tuesday, February 7, 2023

An inductor is an electrical device which oppose the rate of change of current. It is an passive element and the property of material which oppose sudden change in current through it (i.e. oppose sudden fall or rise in current) is called inductance of inductor. Here we will discuss about inductor, inductor symbol and application of inductor. The inductor is also called a coil or a reactor. It is a insulated wire which in a coil form i.e. insulated wire wound in a coil.

Inductor is also capable of storing electrical energy. If a certain amount of current is flowing through it, magnetic filed is induced on it which is varying timely. This magnetic filed help to induce voltage.

The induced voltage is given by:-

v = L di / dt

where L is the inductance of the inductor, v is induced voltage and di / dt is the rate of change in current.

According to Lenz's law, the direction of induced emf is such that it oppose the change in current that created it. so that inductor always oppose the change in current.

# Inductor symbol

The symbol of inductor is given below:-

The inductor has property to oppose change in current which is known as inductance. Inductance is normally represented by L and its SI unit is Henry (H). The value of inductance of a inductor is given by:-

L =  ∅ / I = induced emf / (di /dt)

For N number of turns,

L = N∅ / I

The above equation can be drawn by:-

v = - d(N∅) / dt ------ (i)

v = - L dI /dt = - d (LI) /dt ----(ii)

Now, from (i) and (ii) equation,

- d (N∅) / dt = -d(LI) / dt

or, N∅ = LI

or, L = N∅ / I

where, ∅ = magnetic flux, its SI unit is weber (wb)

The above equation is for self inductance.

For inductance of a solenoid is given by,

Magnetic flux for solenoid is,

∅ = mmf / reluctance

= NI / (l / αμ₀ μ)

Now. inductance,

L = N d∅ / dI

or, L = N d [NI / (l / aμ₀ μ)] / dI

or, L = N x N / (l / aμ₀ μ)

or, L = N² aμ₀ μ/ l

or, L = N² / (l / aμ₀ μ)

∵ L = N² / reluctance

where a = cross-sectional area

μ₀ μ= permittivity of medium

l = length of coil

### Application of inductor

1. Inductor is used as chokes where it allow DC current to pass and block AC current.
2. It is used  in switching operation as energy storage device to produce DC current. (Electrical energy is stored in the inductors and it supplies this energy in switch off time.)
3. It is also used in filter circuit for high pass and low pass frequency filter.
4. It is used in tuned circuit for tunning radio and TV receiver.
5. For power factor correction, it is also used to consume reactive power supplied by capacitor.
6. As we know, it is current limiting device. It is used for limiting switching current and fault current.

### Change of current in RL DC circuit

Let us consider, a DC circuit having a cell of voltage V, inductor of inductance L, resistor of resistance R and switch. As we know inductor acts as current opposing device.

#### 1. Rise of current

When switch is turn on, current will flow in the circuit from battery but it is oppose by inductor i.e. when switch is on, current will sudden goes increase from battery but due to presence of inductor, it allow exponentially increase in current which is given by,
i = I (1 – e-Rt/L)
i = I (1 – e-τ / t)
where τ = L / R

If t = τ then,
i = I (1 - e-1)
or, i =  0.632 I

#### 1. Decay of current

When switch is turn off, current will stop to flow in the circuit from battery but it is oppose by inductor i.e. when switch is off, current will sudden goes decrease at that case but due to presence of inductor, it allow exponentially decrease in current which is given by,
i = I e-Rt/L
i = I e-τ / t = 0.37 I