The Amazing Inductor-Part 2 | How Current Creates A Magnetic Field!

📖Foundation

Philippians 4:13 (KJV)

13 I can do all things through Christ which strengtheneth me.

---

 

Introduction

Welcome back to The Amazing Inductor series!

In Part 1, we learned that an inductor is a coil of insulated wire that stores energy in a magnetic field.

We also explored:

• Air-core inductors
• Iron-core inductors
• Ferrite-core inductors
• Joseph Henry
• Heinrich Lenz
• Why inductance is represented by the letter L
• Why inductance is measured in henrys
• How to build a homemade inductor

In Part 2, we will answer another important question:

How does electric current create a magnetic field?

In this lesson, we’ll explore:

• What a magnetic field is
• How magnetic field lines are represented
• Earth’s magnetic field
• How current flowing through a wire creates magnetism
• Hans Christian Ørsted’s discovery
• Why a coil creates a stronger magnetic field
• How a coil develops North and South magnetic poles
• How reversing current reverses magnetic polarity
• How a moving magnet can generate current
• How current through a coil can deflect a compass

---

Quick Review of Inductors

An inductor is a coil of wire.

When current flows through the coil, a magnetic field forms around it.

That magnetic field allows the inductor to:

• Store energy
• Act as an electromagnet
• Oppose changes in current

Inductance is represented by:

L

The unit of inductance is the:

Henry (H)

An inductor does not simply resist current like a resistor.

Instead:

An inductor resists changes in current.

When current begins increasing, the magnetic field must build.

When current begins decreasing, the magnetic field collapses and attempts to keep current flowing.

---

What Is a Magnetic Field?

A magnetic field is an invisible region around a magnet or a current-carrying conductor where magnetic forces can be detected.

We cannot normally see a magnetic field directly.

However, we can observe its effects.

A magnetic field can:

• Attract certain metals
• Repel or attract another magnet
• Cause a compass needle to move
• Produce force in an electric motor
• Induce voltage in a nearby conductor

A useful comparison is gravity.

We cannot see gravity itself, but we can see what gravity does when an object falls.

In the same way, we cannot see a magnetic field directly, but we can observe how it affects other objects.

---

Magnetic Field Lines

Magnetic fields are often represented using magnetic field lines.

These lines are not physical wires or actual lines floating in space.

They are drawing tools that help us visualize:

• The direction of the magnetic field
• The shape of the magnetic field
• The relative strength of the magnetic field

Outside a bar magnet, magnetic field lines are normally drawn leaving the North pole and curving toward the South pole.

The field lines form complete loops.

They do not begin at one point and simply disappear.

Where the field lines are drawn close together, the magnetic field is stronger.

Where the field lines spread farther apart, the magnetic field is weaker.

The magnetic field is generally strongest near the poles of the magnet.

---

Earth’s Magnetic Field

Earth behaves somewhat like a giant magnet.

Deep inside Earth is a hot, moving outer core made primarily of molten iron and nickel.

The movement of this electrically conductive material generates electric currents.

Those currents help create Earth’s magnetic field.

Earth’s magnetic field extends thousands of miles into space.

It helps protect Earth from charged particles coming from the Sun.

A compass works because its needle is a small magnet.

The compass needle naturally aligns itself with Earth’s magnetic field, allowing us to determine direction.

This shows us something important:

Magnetic fields are not limited to permanent magnets sitting on a workbench.

Magnetic fields exist around Earth, around magnets, and around conductors carrying electric current.

---

Hans Christian Ørsted

Hans Christian Ørsted lived from 1777 to 1851.

In 1820, Ørsted made an important discovery while preparing for a lecture.

A compass happened to be positioned near a wire.

When electric current flowed through the wire, Ørsted noticed that the compass needle moved.

When the current stopped, the compass returned toward its normal position.

This proved that electricity and magnetism are connected.

Ørsted’s discovery showed that:

Electric current creates a magnetic field.

This simple observation helped open the door to the study of electromagnetism.

It eventually helped make possible:

• Electromagnets
• Electric motors
• Generators
• Transformers
• Relays
• Solenoids
• Speakers
• Modern electronic equipment

---

Current Creates a Magnetic Field

Imagine a straight piece of wire.

When no current is flowing through the wire, the wire does not produce a magnetic field caused by current.

When the wire is connected to a power source and current begins flowing, a magnetic field forms around the wire.

The field does not simply travel along the wire.

Instead, it circles around the wire.

The direction of the magnetic field depends on the direction of current flow.

If the direction of current reverses, the direction of the magnetic field also reverses.

The main idea is:

Current flowing through a wire creates a circular magnetic field around that wire.

---

A Straight Wire Does Not Have North and South Poles

A straight current-carrying wire produces a magnetic field that circles around the wire.

However, a straight wire does not behave exactly like a bar magnet.

It does not have one end that is permanently North and another end that is permanently South.

It simply has circular magnetic field lines surrounding it.

North and South poles become more apparent when the wire is wound into a coil.

---

Why Wind the Wire Into a Coil?

Every current-carrying section of wire produces its own magnetic field.

When the wire is wound into a coil, each turn produces a magnetic field.

The magnetic fields from the individual turns reinforce one another.

This creates a stronger, more concentrated magnetic field through the center of the coil.

That is why inductors and electromagnets are made using coils instead of a single straight wire.

A coil behaves much like a bar magnet.

It develops:

• A North pole
• A South pole
• A magnetic field through its center
• Field lines that loop around the outside

Adding an iron or ferrite core can make the magnetic field even stronger.

---

Coil Polarity

When current flows through a coil, one end behaves like a North pole and the other end behaves like a South pole.

The polarity depends on the direction of current through the windings.

If the battery connection is reversed:

• Current flows in the opposite direction
• The magnetic field reverses
• The North and South poles exchange positions

This means the magnetic polarity of an electromagnet can be controlled simply by reversing the direction of current.

---

The Left-Hand Rule

For the method demonstrated in this lesson, the Left-Hand Rule is used with electron-flow direction.

Electron flow is considered from the negative terminal toward the positive terminal.

To use the rule:

1. Determine how the wire is wound around the coil.
2. Follow electron flow from negative to positive.
3. Curl the fingers of your left hand in the direction of current through the turns.
4. Your thumb points toward the North pole of the coil.

If the battery is reversed, electron flow reverses.

The magnetic poles of the coil also reverse.

---

Why an Inductor Resists Changes in Current

When current flows through an inductor, the coil creates a magnetic field.

If the current changes, the magnetic field must also change.

When current begins increasing:

• The magnetic field begins building
• The inductor produces an induced voltage
• That voltage opposes the increase in current

When current begins decreasing:

• The magnetic field begins collapsing
• The inductor produces an induced voltage
• That voltage attempts to keep current flowing

A simple way to remember this is:

An inductor tries to keep current flowing the way it is already flowing.

This behavior will become even more important when we study inductors in LR circuits.

---

Lab 1: Moving a Magnet Through a Coil

The first lab uses:

• A coil of wire
• A permanent magnet
• A sensitive current meter

The meter is connected across the coil.

When the magnet remains still, the meter shows little or no current.

When the magnet moves into the coil, the meter responds.

When the magnet is pulled out of the coil, the meter responds in the opposite direction.

This shows that current direction depends on the direction of the magnet’s motion.

Moving the magnet into the coil generates current in one direction.

Pulling the magnet out generates current in the opposite direction.

Repeatedly moving the magnet in and out causes the meter to move positive and negative.

This produces an alternating current.

The important observation is:

A changing magnetic field can generate electric current in a conductor.

This experiment gives us a preview of electromagnetic induction, which will be explored more deeply in a future lesson.

---

How Generators Use This Principle

Electric generators use the same basic idea.

A generator creates relative motion between:

• A magnetic field
• A coil of wire

The magnet may move while the coil remains stationary.

The coil may move while the magnet remains stationary.

In either case, the changing magnetic field through the coil induces voltage.

This is how mechanical motion can be converted into electrical energy.

---

Lab 2: Ørsted’s Compass Experiment

The second lab recreates the basic principle behind Ørsted’s discovery.

The lab uses:

• A coil of wire
• A battery
• A compass

Before power is applied, the compass aligns with Earth’s magnetic field and points toward North.

The battery is then connected briefly to the coil.

Current flows through the wire and creates a magnetic field.

The compass needle deflects slightly because it is responding to the magnetic field created by the current.

When the battery is disconnected:

• Current stops
• The coil’s magnetic field disappears
• The compass returns toward Earth’s magnetic North

This experiment demonstrates that:

Electric current flowing through a wire or coil creates a magnetic field.

The coil makes the effect easier to observe because the magnetic fields from its individual turns combine and become more concentrated.

---

Lab Safety

Use only a safe, low-voltage battery for this demonstration.

Do not leave a low-resistance coil connected continuously to a battery.

The battery connection should be made only briefly.

Disconnect the circuit if:

• The battery becomes warm
• The wire becomes warm
• A component becomes warm
• You smell overheating insulation

Never connect a homemade coil directly to a household wall outlet.

---

Key Takeaways

• A magnetic field is an invisible region where magnetic forces can be detected.
• Magnetic field lines help us visualize field direction and strength.
• Earth has its own magnetic field.
• A compass needle aligns with a magnetic field.
• Hans Christian Ørsted showed that electricity and magnetism are connected.
• Current flowing through a wire creates a circular magnetic field.
• A straight wire does not have distinct North and South ends.
• Winding the wire into a coil strengthens and concentrates the magnetic field.
• A coil behaves like a bar magnet.
• One end of the coil becomes North and the other becomes South.
• Reversing current reverses the magnetic poles.
• An inductor resists changes in current.
• Moving a magnet through a coil can generate current.
• Current through a coil can deflect a compass.

---

Conclusion

In this lesson, we learned that electricity and magnetism are closely connected.

Electric current flowing through a wire creates a magnetic field.

When the wire is wound into a coil, the magnetic fields from each turn reinforce one another.

This causes the coil to behave like a bar magnet with North and South poles.

Reversing the current reverses those magnetic poles.

We also saw two important lab demonstrations.

First, moving a magnet through a coil generated current in two different directions.

Second, applying current to a coil created a magnetic field strong enough to deflect a compass needle.

These ideas form the foundation for understanding:

• Inductors
• Electromagnets
• Transformers
• Electric motors
• Generators
• LR circuits
• Electromagnetic induction

Whoo Buddy!!