Course: From Basic Science to Web Hosting

Module 01 — Basic Science

What Is Inductance?

Difficulty: Beginner
Prerequisites: Lesson 007 — What Is Capacitance?
Estimated time: 20 minutes

1. Learning Objectives

After this lesson, you should understand:

What inductance is
What an inductor is
The relationship between current and magnetic fields
How an inductor stores energy
Why an inductor opposes changes in current
The difference between resistance, capacitance, and inductance
Why inductors are important in power supplies and electronics

2. Start With Current

We learned:

Voltage
   ↓
Electric field
   ↓
Charge carriers respond
   ↓
Current

Now ask:

What happens around a wire when current flows?

A current produces a magnetic field.

Conceptually:

Electric current
      ↓
Magnetic field

This is the foundation of inductance.

3. What Is a Magnetic Field?

A magnetic field describes the magnetic influence in a region of space.

Around a straight current-carrying wire:

        ↺
     ↺  │  ↻
   ↺    │    ↻
        │
        │
      Current

The magnetic field forms circular patterns around the conductor.

The direction can be determined using the right-hand rule.

4. What Is an Inductor?

An inductor is an electrical component designed to store energy in a magnetic field.

A simple inductor is often made from a coil of wire:

       ┌─────────┐
───────(((((((((──────
       └─────────┘

When current flows through the coil:

Current
   ↓
Magnetic field
   ↓
Stored magnetic energy

5. What Is Inductance?

Inductance describes how strongly a circuit element opposes changes in current.

The symbol is:

The unit is:

Henry (H)

For an ideal inductor:

V = L(di/dt)

where:

V = voltage
L = inductance
di/dt = rate of change of current

6. The Most Important Idea

An inductor does not simply oppose current.

It opposes changes in current.

This distinction is very important.

Current constant
      ↓
Ideal inductor voltage = 0

but:

Current changing rapidly
      ↓
Large induced voltage

7. Why Does This Happen?

When current through a conductor changes:

Changing current
      ↓
Changing magnetic field
      ↓
Induced voltage

This behavior is described by Faraday’s law of electromagnetic induction.

The induced effect acts in a direction that opposes the change producing it, consistent with Lenz’s law.

8. Example

Suppose an inductor has:

L = 1 H

and the current changes at:

di/dt = 2 A/s

Then:

V = L(di/dt)

V = 1 × 2

V = 2 V

The idealized induced voltage magnitude is:

2 V

The actual polarity depends on the direction of the current change.

9. Inductor Energy

An ideal inductor stores energy in its magnetic field.

The equation is:

E = ½LI²

where:

E = energy
L = inductance
I = current

Notice the similarity to a capacitor:

Capacitor:

E = ½CV²

Inductor:

E = ½LI²

10. Capacitor vs Inductor

This is one of the most useful comparisons in basic electronics.

Component	Stores energy in	Opposes
Resistor	Does not ideally store energy	Current/voltage relationship through dissipation
Capacitor	Electric field	Change in voltage
Inductor	Magnetic field	Change in current

Simplified:

Resistor
   ↓
Dissipation

Capacitor
   ↓
Electric field

Inductor
   ↓
Magnetic field

11. What Happens When Current Starts?

Suppose an inductor is initially carrying zero current.

You suddenly apply a voltage.

The inductor doesn’t allow its current to jump instantaneously in the idealized model.

Instead:

Voltage applied
      ↓
Current begins increasing
      ↓
Magnetic field builds
      ↓
Energy stored

The current changes progressively according to the circuit.

12. What Happens When Power Is Removed?

Suppose current is flowing through an inductor.

Now disconnect the source.

The magnetic field begins collapsing.

Stored magnetic energy
       ↓
Collapsing magnetic field
       ↓
Induced voltage
       ↓
Energy released into circuit

This can create a large voltage spike if the current has no safe path to continue.

13. Why Relays and Motors Matter

Inductive loads include:

Motors
Relays
Transformers
Solenoids
Coils

When current through these devices changes suddenly, the resulting induced voltage can be significant.

This is why circuits controlling relay coils often include protective components such as a flyback diode.

We will study this later.

14. Inductor in a DC Circuit

Consider:

Battery ── R ── L

When the circuit is switched on:

Current starts
     ↓
Inductor resists rapid increase
     ↓
Current gradually approaches its steady value

For a simple RL circuit:

τ = L/R

This is the RL time constant.

15. Compare RC and RL

We now have:

RC circuit

τ = RC

RL circuit

τ = L/R

Both introduce time-dependent behavior.

R + C
 ↓
Electric-field storage

R + L
 ↓
Magnetic-field storage

16. Why Are Inductors Used?

Inductors are used in:

Power supplies
Filters
Transformers
Radio circuits
Oscillators
DC-DC converters
Motors
EMI filtering

17. Inductors in Power Supplies

A simplified switching power supply may contain:

Input
  ↓
Switching circuit
  ↓
Inductor
  ↓
Capacitor
  ↓
Regulated output

The inductor and capacitor work together to store and transfer energy and reduce unwanted voltage/current variation.

This is extremely important in computers and servers.

18. Inductor + Capacitor

Now we have two energy-storage components:

Capacitor
   ↓
Electric field

Inductor
   ↓
Magnetic field

When combined:

L + C
 ↓
Resonance
 ↓
Filters
 ↓
Oscillators
 ↓
Communication circuits

This becomes important later when we study networking and radio signals.

19. Resonance

An LC circuit can exchange energy between:

Electric field
      ↕
Magnetic field

Conceptually:

Capacitor
   ↓
Electric energy
   ↓
Inductor
   ↓
Magnetic energy
   ↓
Capacitor
   ↓
...

This exchange can produce oscillatory behavior.

20. Why This Matters for Communication

Communication systems use electrical and electromagnetic signals.

Those signals often require:

Filtering
Frequency selection
Oscillation
Impedance matching
Signal conditioning

Inductors and capacitors are important components in these functions.

This eventually connects to:

Electronic communication
 ↓
Networking
 ↓
Internet

21. The Three Basic Passive Components

You now know the three fundamental passive circuit elements:

          CIRCUITS
             │
     ┌───────┼───────┐
     ↓       ↓       ↓
 Resistor Capacitor Inductor
     │       │       │
     ↓       ↓       ↓
Dissipation Electric  Magnetic
           field      field
             │         │
             └────┬────┘
                  ↓
              Electronics

22. Their Basic Equations

Resistor

V = IR

Capacitor

i = C(dV/dt)

Inductor

V = L(di/dt)

These three equations form a major foundation for circuit analysis.

23. A Deeper Connection

Notice the pattern:

Resistor:
Voltage ↔ Current

Capacitor:
Current ↔ Change in Voltage

Inductor:
Voltage ↔ Change in Current

This tells us that circuits are not merely about “electricity flowing.”

They are systems in which:

Voltage
Current
Electric field
Magnetic field
Energy
Time

interact with one another.

24. From Basic Electricity to Electronics

Our learning path is now:

Matter
 ↓
Atom
 ↓
Electron
 ↓
Charge
 ↓
Electric field
 ↓
Voltage
 ↓
Current
 ↓
Circuit
 ↓
Resistance
 ↓
Capacitance
 ↓
Inductance
 ↓
RLC circuits
 ↓
Signals
 ↓
Electronics

The next step is where things become much more directly connected to computers:

Materials
 ↓
Conductors
 ↓
Insulators
 ↓
Semiconductors

25. Quick Check

What does an inductor store?

Energy in a magnetic field.

What does inductance oppose?

Changes in current.

Unit of inductance?

Henry (H).

Energy stored?

E = ½LI²

Voltage-current relationship?

V = L(di/dt)

RC time constant?

τ = RC

RL time constant?

τ = L/R

Next Lesson

Lesson 009 — What Is a Semiconductor?

This is a major transition.

We will study:

Conductors
      ↓
Insulators
      ↓
Semiconductors
      ↓
Silicon
      ↓
Crystal structure
      ↓
Valence electrons
      ↓
Energy bands
      ↓
Band gap
      ↓
Doping
      ↓
P-type
      ↓
N-type
      ↓
Diode
      ↓
Transistor
      ↓
Computer chip

This is the point where our basic science course starts becoming semiconductor and computer engineering.

CresignSys Learn — Lesson 008