Chapter 13: Magnets 🧲
A Comprehensive Guide for PSTET Paper-2 (Science)
Chapter Overview
| Section | Topic | PSTET Weightage | Page No. |
|:---:|:---|::---:|:---:|
| 13.1 | Discovery of Magnets and Magnetic Materials | Medium | 2 |
| 13.2 | Types of Magnets (Natural and Artificial) | High | 6 |
| 13.3 | Poles of a Magnet and Magnetic Attraction/Repulsion | High | 10 |
| 13.4 | Finding Directions with a Magnet | Medium | 15 |
| 13.5 | Making a Magnet | Medium | 18 |
| 13.6 | Earth as a Giant Magnet | High | 23 |
| Practice Zone | MCQs & Pedagogical Questions | - | 28 |
Learning Objectives 🎯
After studying this chapter, you will be able to:
✅ Trace the historical discovery of magnets and identify magnetic materials
✅ Differentiate between natural and artificial magnets with examples
✅ Explain the concept of magnetic poles and the law of magnetic attraction/repulsion
✅ Demonstrate how a magnet can be used to find directions
✅ Describe various methods of making magnets (single-touch, double-touch, induction, electrical)
✅ Explain the concept of Earth as a giant magnet and its importance in navigation
✅ Apply pedagogical strategies to teach magnetism effectively to upper primary students
Pedagogical Link 🔗
For Teachers: This chapter directly aligns with:
Class 6 Science NCERT Chapter 13: "Fun with Magnets"
Teaching Tips:
Begin with a "Mystery Box" activity—students guess what's inside by how it attracts paper clips
Create a "Magnetic Materials Discovery Station" with various objects for testing
Use iron filings to visualize magnetic field patterns (sprinkle on paper over magnet)
Conduct compass-making activities using magnetized needles and water
Connect to history and geography when discussing navigation and Earth's magnetism
Section 13.1: Discovery of Magnets and Magnetic Materials 🏔️
Introduction
The story of magnets begins thousands of years ago with a curious rock that had the magical power to attract iron. This rock, called lodestone or magnetite, was humanity's first introduction to the mysterious world of magnetism .
13.1.1 The Legend of Magnes
According to ancient Greek legend, a shepherd named Magnes was tending his sheep in a region of northern Greece called Magnesia. As he walked, the iron tip of his staff and the iron nails in his sandals were pulled toward a large black rock. This rock, which attracted iron, was later named magnetite after either the shepherd or the region .
Historical Fact: Whether the story is true or not, the region of Magnesia in Greece does contain large deposits of magnetite, and the word "magnet" likely comes from this region .
13.1.2 Early Discoveries in China
The Chinese were among the first to observe and document magnetic phenomena :
| Period | Development |
|---|---|
| 2600-2300 BCE | Natural magnetic iron ore (Fe₃O₄) was first discovered |
| 4th Century BCE | A book called "Book of the Devil Valley Master" noted: "The lodestone attracts iron" |
| 2nd Century BCE | The first magnetic compasses were made using lodestone |
📝 PSTET Note: The earliest mention of a needle attracted to a lodestone appears in a Chinese text published around 80 CE .
13.1.3 Ancient Names for Magnets
Chinese Tradition: The Chinese originally called magnets "Ci Shi" (慈石)—meaning "loving stone" or "motherly stone." They believed the magnet loved iron like a mother loves her child, pulling it close .
Other Ancient Names:
Hercules Stone (by Greeks)
Iron Stone (by various cultures)
13.1.4 Understanding Magnetic Materials
A. What are Magnetic Materials?
Definition: Magnetic materials are substances that are attracted to magnets and can themselves be magnetized .
The Magnetic Elements: Only three elements are naturally magnetic at room temperature :
| Element | Symbol | Magnetic Property |
|---|---|---|
| Iron | Fe | Strongly magnetic (ferromagnetic) |
| Nickel | Ni | Strongly magnetic (ferromagnetic) |
| Cobalt | Co | Strongly magnetic (ferromagnetic) |
Other Magnetic Materials:
Steel (alloy of iron and carbon)
Alnico (alloy of aluminum, nickel, cobalt, and iron)
Neodymium (rare earth element used in powerful magnets)
B. Non-Magnetic Materials
Definition: Non-magnetic materials are substances that are not attracted to magnets and cannot be magnetized .
Examples of Non-Magnetic Materials:
Wood, plastic, rubber, glass, paper, cloth
Copper, aluminum, gold, silver, brass
Water, air, stone
🧪 Classroom Activity: Magnetic Material Hunt
| Step | Procedure |
|---|---|
| 1 | Give students a magnet and a collection of various objects |
| 2 | Ask them to predict which objects will be attracted |
| 3 | Test each object by bringing the magnet close |
| 4 | Record results in a table |
Sample Recording Table:
| Object | Material | Attracted? (Yes/No) | Magnetic/Non-Magnetic |
|---|---|---|---|
| Paper clip | Steel | Yes | Magnetic |
| Aluminum foil | Aluminum | No | Non-magnetic |
| Copper coin | Copper | No | Non-magnetic |
| Iron nail | Iron | Yes | Magnetic |
| Plastic ruler | Plastic | No | Non-magnetic |
13.1.5 The Mystery of Magnetism Explained
For centuries, people had no explanation for why magnets worked. Ancient Greek philosopher Thales of Miletus (6th century BCE) believed magnets possessed souls .
Modern Explanation: Magnetism is caused by the movement of electrons within atoms. In magnetic materials, tiny regions called magnetic domains align their electrons in the same direction, creating a net magnetic field .
13.1.6 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Storytelling | Tell the legend of Magnes to capture interest | Engaging introduction |
| Historical Timeline | Create a timeline of magnet discoveries | Cross-curricular (history) |
| Material Testing Station | Test various objects to classify as magnetic/non-magnetic | Hands-on investigation |
| "Magnetic or Not?" Game | Quick classification activity | Formative assessment |
Section 13.2: Types of Magnets (Natural and Artificial) 🔧
Introduction
Magnets can be broadly classified into two main categories based on their origin: natural magnets found in the earth and artificial magnets made by humans .
13.2.1 Natural Magnets
Definition: Natural magnets are magnets that are found naturally in the earth's crust .
The Only Natural Magnet: The only naturally occurring magnetic material is magnetite (Fe₃O₄), also called lodestone .
Characteristics of Natural Magnets:
Irregular shape (not manufactured)
Relatively weak magnetic strength
Found in various parts of the world
May have been naturally magnetized by lightning strikes
📝 PSTET Note: A lodestone is a rock rich in magnetite that has become magnetized naturally .
13.2.2 Artificial Magnets
Definition: Artificial magnets are magnets made by humans from magnetic materials .
Why Artificial Magnets?
Can be made in any desired shape and size
Can be made much stronger than natural magnets
Can be manufactured consistently and reliably
Shapes of Artificial Magnets:
| Shape | Description | Common Uses |
|---|---|---|
| Bar Magnet 🧲 | Rectangular bar with poles at ends | School laboratories, compass needles |
| Horse-shoe (U-shaped) Magnet | Bent like a horseshoe | Lifting heavy objects, older radios |
| Ring Magnet | Circular ring | Speakers, motors |
| Cylindrical Magnet | Rod-shaped | Various applications |
| Button/Disc Magnet | Flat, circular | Refrigerator magnets, crafts |
| Magnetic Needle | Thin, pointed | Compasses |
13.2.3 Permanent vs. Temporary Magnets
Artificial magnets can be further classified based on how long they retain their magnetism :
A. Permanent Magnets
Definition: Permanent magnets retain their magnetic properties over a long period of time .
Characteristics:
Made from hard magnetic materials (like steel)
Difficult to magnetize but retain magnetism well
Do not lose magnetism easily
Examples:
Bar magnets
Horse-shoe magnets
Alnico magnets
Ceramic (ferrite) magnets
Rare-earth magnets (neodymium, samarium-cobalt)
B. Temporary Magnets
Definition: Temporary magnets lose their magnetic properties after the magnetizing influence is removed .
Characteristics:
Made from soft magnetic materials (like soft iron)
Easy to magnetize but lose magnetism quickly
Act as magnets only while near a permanent magnet or in a magnetic field
Examples:
Iron nails attracted to a magnet become temporary magnets
Electromagnets (when current flows)
Paper clips while stuck to a magnet
Table 13.1: Permanent vs. Temporary Magnets
| Feature | Permanent Magnet | Temporary Magnet |
|---|---|---|
| Material | Hard magnetic materials (steel) | Soft magnetic materials (iron) |
| Retention | Retains magnetism for long time | Loses magnetism quickly |
| Magnetization | Difficult to magnetize | Easy to magnetize |
| Demagnetization | Resists demagnetization | Easily demagnetized |
| Examples | Bar magnet, horse-shoe magnet | Iron nail, paper clip on magnet |
13.2.4 Modern Artificial Magnets by Composition
Since the 20th century, scientists have developed various types of artificial magnets with different properties :
| Type | Composition | Characteristics | Developed |
|---|---|---|---|
| Alnico Magnets | Aluminum, Nickel, Cobalt, Iron | Strong, temperature stable, expensive | 1930s |
| Ferrite (Ceramic) Magnets | Iron oxide, Strontium/Barium | Low cost, corrosion-resistant, brittle | 1950s |
| Samarium-Cobalt Magnets | Samarium, Cobalt | Very strong, high temperature stability, very expensive | 1960s-70s |
| Neodymium Magnets | Neodymium, Iron, Boron | Extremely strong (strongest type), can corrode | 1980s |
🌍 Did You Know? Neodymium magnets are so strong that two magnets can shatter if they snap together from a distance!
13.2.5 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Magnet Collection | Show different shapes of magnets to students | Visual recognition |
| Compare and Contrast | Compare permanent vs. temporary magnets | Analytical thinking |
| Temporary Magnet Demo | Show how an iron nail can pick up paper clips only when touching a magnet | Hands-on demonstration |
| Sorting Activity | Sort given magnets into categories | Classification skills |
Section 13.3: Poles of a Magnet and Magnetic Attraction/Repulsion 🔄
Introduction
Every magnet, regardless of its shape or size, has two special points where its magnetic force is strongest. These points are called poles. Understanding poles and how they interact is fundamental to understanding magnetism .
13.3.1 What are Magnetic Poles?
Definition: Magnetic poles are the regions in a magnet where the magnetic force is strongest .
Characteristics of Poles:
They occur in pairs—every magnet has two poles
The poles are of equal strength
They are usually located near the ends of a magnet
Visual Demonstration: If you dip a bar magnet in iron filings, you'll see the filings cluster most thickly at the ends—showing where the poles are located .
13.3.2 Naming the Poles: North and South
The poles are named based on how the magnet behaves when freely suspended :
| Pole | Full Name | Behavior When Suspended |
|---|---|---|
| North Pole (N) | North-seeking pole | Points toward geographic north |
| South Pole (S) | South-seeking pole | Points toward geographic south |
Important Convention:
The end that points north is called the North Pole of the magnet
The end that points south is called the South Pole of the magnet
📝 PSTET Note: This naming convention comes from navigational use—the pole that seeks north is called the north pole .
13.3.3 The Law of Magnetic Poles
Fundamental Law: Like poles repel each other; unlike poles attract each other .
Table 13.2: Magnetic Pole Interactions
| Interaction | Result | Why? |
|---|---|---|
| N + N | Repel | Like poles |
| S + S | Repel | Like poles |
| N + S | Attract | Unlike poles |
Simple Demonstration:
| Step | Action | Observation |
|---|---|---|
| 1 | Take two bar magnets marked N and S | - |
| 2 | Bring two N poles close together | They push apart (repel) |
| 3 | Bring two S poles close together | They push apart (repel) |
| 4 | Bring N pole near S pole | They pull together (attract) |
13.3.4 The Most Important Fact: Poles Always Come in Pairs
Key Principle: If you break a magnet into pieces, each piece becomes a complete magnet with both a north and a south pole .
Demonstration:
Original Bar Magnet:
[ N ========= S ]
↓ (break)
[ N = S ] [ N = S ]Why This Happens:
Magnets are made of tiny molecular magnets (domains) aligned in the same direction
Each tiny magnet has both N and S poles
Breaking the magnet doesn't destroy these tiny magnets—they just rearrange slightly
📝 PSTET Note: This is a key difference between magnetic poles and electric charges. Electric charges (positive and negative) can exist separately, but magnetic poles always come in pairs .
13.3.5 Magnetic Field and Field Lines
Definition: The magnetic field is the region around a magnet where its magnetic force can be detected .
Properties of Magnetic Field Lines:
| Property | Description |
|---|---|
| Direction | Outside the magnet, field lines go from N pole to S pole |
| Inside the magnet | Field lines continue from S pole to N pole (forming closed loops) |
| Strength indication | Closer lines = stronger field; spread lines = weaker field |
| Never cross | Field lines never intersect each other |
Visualizing Magnetic Field:
| Method | Procedure |
|---|---|
| Iron Filings Method | Place paper over magnet, sprinkle iron filings, tap gently—filings align along field lines |
| Compass Method | Place small compasses around magnet—needles point along field lines |
Field Patterns for Different Situations:
| Situation | Field Pattern |
|---|---|
| Single bar magnet | Curved lines from N to S, concentrated at poles |
| Two like poles facing (N-N) | Field lines push apart, showing repulsion |
| Two unlike poles facing (N-S) | Field lines connect, showing attraction |
13.3.6 Testing if an Object is a Magnet
The Sure Test: Repulsion is the only sure test of magnetism .
Why Repulsion is the Only Sure Test:
| Test | Result with Magnet | Result with Magnetic Material |
|---|---|---|
| Bring N pole near | If N of unknown, repels; if S of unknown, attracts | Always attracts (no repulsion) |
| Bring S pole near | If S of unknown, repels; if N of unknown, attracts | Always attracts (no repulsion) |
Conclusion:
If an object repels a known pole, it must be a magnet
Attraction alone is not proof (magnets attract magnetic materials)
13.3.7 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Pole Identification | Students find N and S poles using suspended magnet | Hands-on learning |
| Magnetic Field Visualization | Sprinkle iron filings on paper over magnet | Visual learning |
| "Magnet or Not?" Challenge | Test objects using repulsion test | Critical thinking |
| Breaking a Magnet Demo | Show (or describe) what happens when magnet breaks | Conceptual understanding |
Section 13.4: Finding Directions with a Magnet 🧭
Introduction
One of the most important uses of magnets throughout history has been for navigation. A freely suspended magnet always aligns itself in a north-south direction, making it a simple but effective compass .
13.4.1 How a Magnet Finds Direction
Principle: When a magnet is free to rotate (suspended by a thread or floated on water), it comes to rest with its north pole pointing toward the geographic north of the Earth .
Why This Happens:
The Earth itself behaves like a giant magnet
It has its own magnetic poles
The north pole of a magnet is attracted to the Earth's magnetic south pole (located near geographic north)
📝 PSTET Note: This is a common point of confusion—the Earth's magnetic pole near geographic north is actually a south-seeking pole because it attracts the north pole of a compass needle .
13.4.2 The Magnetic Compass
Definition: A magnetic compass is an instrument that uses a magnetized steel bar to indicate direction relative to the Earth's magnetic poles .
Parts of a Simple Compass:
| Part | Function |
|---|---|
| Magnetic Needle | Freely rotating magnet (usually marked N at one end) |
| Pivot | Allows needle to rotate with minimal friction |
| Compass Card | Marked with directions (N, S, E, W) |
| Housing | Protective case, often transparent |
13.4.3 Making a Simple Compass
Activity 13.1: Making a Floating Compass
| Step | Procedure |
|---|---|
| 1 | Magnetize a sewing needle by stroking it with a magnet (50 times in one direction) |
| 2 | Push the magnetized needle through a small piece of cork or foam |
| 3 | Fill a shallow dish with water |
| 4 | Float the cork with needle on the water surface |
| 5 | Observe which direction the needle points |
Observation: The needle will rotate and come to rest pointing approximately north-south.
Why It Works:
The floating setup allows free rotation with minimal friction
The Earth's magnetic field exerts torque on the magnetized needle
The needle aligns with the field lines
13.4.4 Finding All Directions
Once you know north, you can find all other directions :
| If you face... | Behind you is... | Left is... | Right is... |
|---|---|---|---|
| North | South | West | East |
| South | North | East | West |
| East | West | North | South |
| West | East | South | North |
Simple Rule: North → South opposite; East → West opposite.
13.4.5 History of Magnetic Compass
🌍 Did You Know? The magnetic compass is considered one of China's Four Great Inventions.
13.4.6 Limitations of Magnetic Compass
| Limitation | Explanation |
|---|---|
| Magnetic declination | Magnetic north and true north are not the same; varies by location |
| Local interference | Nearby iron/steel objects can affect readings |
| Can't use near magnetic poles | Compass becomes unreliable near magnetic poles |
| Not accurate on ships | Ship's metal affects compass (corrected with special adjustments) |
13.4.7 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Make Your Own Compass | Students make floating compasses | Hands-on learning |
| Compass Treasure Hunt | Hide treasure; give directions using compass | Engaging application |
| Historical Connection | Discuss role of compass in exploration | Cross-curricular |
| Compare Directions | Use compass to find directions in school | Real-world application |
Section 13.5: Making a Magnet 🔨
Introduction
Magnets can be made from magnetic materials using various methods. These methods work by aligning the tiny magnetic domains within the material in the same direction .
13.5.1 The Molecular Theory of Magnetism
Weber's Theory (Molecular Magnet Theory):
Every magnetic material is composed of tiny molecular magnets
In unmagnetized material, these molecular magnets point in random directions—their magnetic effects cancel out
In magnetized material, the molecular magnets align with their north poles pointing in the same direction
Visual Representation:
Unmagnetized: ↑ ↓ → ← ↙ ↗ ↘ ↖ (random) Magnetized: ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ (aligned)
13.5.2 Methods of Making Magnets
There are three main methods to make magnets :
A. Single-Touch Method
Procedure:
| Step | Action |
|---|---|
| 1 | Place the iron/steel bar to be magnetized on a table |
| 2 | Take a strong bar magnet |
| 3 | Place one pole (say N) at one end of the bar |
| 4 | Stroke firmly along the bar to the other end |
| 5 | Lift the magnet well away from the bar |
| 6 | Repeat 30-50 times, always stroking in the same direction |
Important Rules:
Always stroke in the same direction (never back and forth)
Lift the magnet away after each stroke before starting again
The end where the stroke ends gets opposite polarity to the stroking pole
Result: The bar becomes magnetized.
B. Double-Touch Method
Procedure:
| Step | Action |
|---|---|
| 1 | Place the bar to be magnetized on a table |
| 2 | Take two bar magnets |
| 3 | Place opposite poles of the two magnets together at the center of the bar |
| 4 | Draw them apart toward opposite ends simultaneously |
| 5 | Lift both magnets well away |
| 6 | Repeat several times |
Advantage: This method produces stronger magnetization than single-touch method.
C. Induction Method
Procedure:
| Step | Action |
|---|---|
| 1 | Place the iron/steel bar in contact with a strong permanent magnet |
| 2 | Leave it in contact for some time |
| 3 | Remove it and test |
Explanation: When a magnetic material touches a magnet, some of the magnetic domains align, making the material a temporary magnet .
Example: An iron nail stuck to a magnet can pick up other paper clips—it has become magnetized by induction.
D. Electrical Method (Using Electricity)
Procedure:
Result: The object becomes magnetized.
Advantages of Electrical Method:
Can produce very strong magnets
Magnetic polarity can be reversed by reversing current
Magnetism can be controlled by current
13.5.3 Which Materials Make Good Magnets?
For Permanent Magnets:
Use hard magnetic materials like steel
Hard to magnetize but retain magnetism
Example: Steel knife blade
For Temporary Magnets:
Use soft magnetic materials like soft iron
Easy to magnetize but lose magnetism quickly
Example: Electromagnet cores
13.5.4 Demagnetization
Magnets can lose their magnetism through :
| Cause | Explanation |
|---|---|
| Heating | Heating above Curie temperature randomizes domains |
| Hammering/Dropping | Physical shock disrupts domain alignment |
| Strong opposing field | External field can reverse/randomize domains |
| Time | Very old magnets may weaken (especially steel magnets) |
Storage of Magnets:
Store with keepers (soft iron pieces across poles)
Keep unlike poles together when storing multiple magnets
Avoid dropping or heating magnets
13.5.5 The Curie Temperature
Definition: The Curie temperature (or Curie point) is the temperature above which a magnetic material loses its magnetism .
| Material | Curie Temperature (approximate) |
|---|---|
| Iron | 770°C (1390°F) |
| Nickel | 358°C |
| Cobalt | 1130°C |
What Happens: Above the Curie temperature, thermal energy overcomes the forces keeping domains aligned—domains become random and material becomes non-magnetic .
13.5.6 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Make a Magnet Activity | Students make magnets using stroking method | Hands-on learning |
| Induction Demonstration | Show paper clips hanging from magnetized nail | Visual learning |
| Compare Methods | Compare strength of magnets made by different methods | Scientific investigation |
| Domain Model | Use students as "magnetic domains" to demonstrate alignment | Kinesthetic learning |
Section 13.6: Earth as a Giant Magnet 🌍
Introduction
The Earth itself behaves like a giant magnet, with a magnetic field extending far into space. This is why compasses work—the Earth's magnetic field exerts a force on magnetized needles, causing them to align in a north-south direction .
13.6.1 Evidence that Earth is a Magnet
| Evidence | Explanation |
|---|---|
| Compass behavior | Freely suspended magnets align north-south everywhere on Earth |
| Auroras | Charged particles from Sun follow Earth's magnetic field to poles, creating auroras |
| Magnetic rocks | Ancient rocks preserve record of Earth's magnetic field |
| Magnetic surveys | Instruments detect variations in Earth's magnetic field |
13.6.2 Earth's Magnetic Poles
Important Fact: Earth's magnetic poles are NOT the same as its geographic poles .
| Type | Location | Description |
|---|---|---|
| Geographic North Pole | Northern axis point | True north; axis of rotation |
| Geographic South Pole | Southern axis point | True south |
| Magnetic North Pole | Northern Canada (currently) | Where field lines point vertically down; moves slowly |
| Magnetic South Pole | Off coast of Antarctica | Where field lines point vertically up; moves slowly |
Current Locations:
Magnetic North Pole: ~86°N, 175°W (in Arctic Canada; moving toward Russia)
Magnetic South Pole: ~64°S, 136°E (off coast of Antarctica)
13.6.3 The Magnetic Pole Confusion
The Key Point: The north pole of a compass needle points toward the Earth's magnetic pole located in the Arctic. But this means that the magnetic pole near the geographic north pole must be a south-seeking pole magnetically !
Table 13.3: Earth's Magnetic Poles Explained
| Location | Geographic Name | Magnetic Polarity | Attracts |
|---|---|---|---|
| Near Geographic North | North Pole | South magnetic pole | North pole of compass |
| Near Geographic South | South Pole | North magnetic pole | South pole of compass |
Simple Memory Aid:
Opposites attract: N pole of magnet points to Earth's magnetic S pole
Earth's magnetic S pole is near geographic N pole
13.6.4 Magnetic Declination
Definition: Magnetic declination is the angle between geographic north (true north) and magnetic north at a given location .
Why Declination Matters:
Compasses point to magnetic north, not true north
Navigators must adjust for declination to find true north
Declination varies by location and changes over time
Declination in India:
Varies from about 0° to 3° east depending on location
Relatively small compared to high-latitude regions
13.6.5 Earth's Magnetic Field
Characteristics of Earth's Magnetic Field :
| Feature | Description |
|---|---|
| Shape | Similar to field of a giant bar magnet inside Earth |
| Strength | About 0.25 to 0.65 Gauss (25-65 μT) |
| Source | Motion of molten iron in Earth's outer core (dynamo effect) |
| Protection | Deflects solar wind, protects atmosphere |
| Variation | Changes over time; reverses polarity every few hundred thousand years |
The Magnetosphere: The region of space dominated by Earth's magnetic field. It extends tens of thousands of kilometers into space and protects us from harmful solar radiation .
13.6.6 Magnetic Reversals
Fact: Earth's magnetic field has reversed polarity hundreds of times throughout history .
What Happens During a Reversal:
Magnetic north becomes magnetic south, and vice versa
The field weakens during reversal but doesn't disappear completely
Reversals take thousands of years
Last reversal was about 780,000 years ago
Evidence: Magnetic minerals in volcanic rocks record the direction of Earth's field at the time they cooled.
13.6.7 Why Is Earth Magnetic?
The Dynamo Theory:
Earth's core consists of molten iron and nickel
This liquid metal circulates due to heat from the inner core
The motion of electrically conductive fluid in presence of Earth's rotation creates electric currents
These electric currents generate magnetic field
13.6.8 Planets and Their Magnetic Fields
| Planet | Magnetic Field | Reason |
|---|---|---|
| Earth | Strong | Liquid iron core, rapid rotation |
| Jupiter | Very strong | Metallic hydrogen, rapid rotation |
| Mars | Weak, localized | Small, mostly solid core |
| Venus | Very weak | Slow rotation, possibly solid core |
| Mercury | Weak but present | Partially liquid core |
13.6.9 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Globe Demonstration | Show geographic vs. magnetic poles on globe | Visual learning |
| Compass Around World | Discuss how compass behaves in different locations | Critical thinking |
| Magnetic Declination Activity | Find declination for your location using online resources | Real-world application |
| Aurora Videos | Show videos of auroras; explain connection to Earth's magnetic field | Engaging visual |
Chapter Summary: Key Points for Revision 📝
Quick Revision Table
| Topic | Key Points | Common PSTET Questions |
|---|---|---|
| Discovery | Magnetite (Fe₃O₄) found in Magnesia, Greece; Chinese called it "loving stone" | Who discovered magnets? |
| Magnetic Materials | Iron, nickel, cobalt, steel; non-magnetic: wood, plastic, copper, aluminum | Give examples of magnetic/non-magnetic materials |
| Natural Magnets | Found in nature (lodestone/magnetite); irregular shape, weak | What is a natural magnet? |
| Artificial Magnets | Made by humans; various shapes (bar, horseshoe, ring) | Name different magnet shapes |
| Permanent Magnets | Retain magnetism; made of steel/hard materials | Examples of permanent magnets |
| Temporary Magnets | Lose magnetism quickly; made of soft iron | What is a temporary magnet? |
| Magnetic Poles | N and S poles; like poles repel, unlike attract | State law of magnetic poles |
| Breaking Magnets | Each piece becomes complete magnet with both poles | What happens when you break a magnet? |
| Finding Directions | Freely suspended magnet points N-S; used in compass | How does a compass work? |
| Making Magnets | Single-touch, double-touch, induction, electrical methods | Describe single-touch method |
| Earth as Magnet | Earth has magnetic field; magnetic poles near geographic poles | Why does a compass point north? |
| Magnetic Declination | Angle between true north and magnetic north | What is magnetic declination? |
Practice Zone: PSTET-Style Questions 🎯
Content-Based MCQs
Q1. The only naturally occurring magnetic material is:
a) Iron
b) Nickel
c) Magnetite
d) Cobalt
Q2. Which of the following is a non-magnetic material?
a) Iron nail
b) Steel spoon
c) Copper coin
d) Nickel coin
Q3. When a magnet is freely suspended, it comes to rest pointing in which direction?
a) East-West
b) North-South
c) Random direction
d) Depends on magnet size
Q4. Like poles of two magnets:
a) Attract each other
b) Repel each other
c) Have no effect
d) Sometimes attract, sometimes repel
Q5. If you break a bar magnet into two pieces, you will get:
a) One piece with N pole only, other with S pole only
b) Two pieces with no magnetism
c) Two complete magnets, each with N and S poles
d) One piece with stronger magnetism
Q6. The sure test of magnetism is:
a) Attraction
b) Repulsion
c) Color
d) Weight
Q7. Earth's magnetic field is generated by:
a) Solar wind
b) Molten iron in outer core
c) Ocean currents
d) Atmospheric pressure
Q8. The north pole of a compass needle points toward:
a) Geographic North Pole
b) Magnetic North Pole (which is magnetically south)
c) Geographic South Pole
d) Magnetic South Pole
Q9. Which method of making magnets uses electricity?
a) Single-touch method
b) Double-touch method
c) Induction method
d) Electrical method (solenoid)
Q10. Heating a magnet above its Curie temperature causes it to:
a) Become stronger
b) Become permanently magnetized
c) Lose its magnetism
d) Reverse its poles
Pedagogical MCQs
Q11. A teacher wants to demonstrate that like poles repel. The best activity would be:
a) Show a diagram in textbook
b) Bring two bar magnets and let students bring like poles together to feel repulsion
c) Lecture about it
d) Show a video only
Q12. To introduce the topic of magnets to Class 6 students, the most engaging approach would be:
a) Start with definition and properties
b) Give students magnets and various objects to explore freely first
c) Write notes on board
d) Show pictures of magnets
Q13. A student asks, "Why does a compass always point north?" The teacher should explain using:
a) "That's how it's made"
b) Earth behaves like a giant magnet, and compass aligns with Earth's magnetic field
c) "I don't know"
d) "It's magic"
Q14. While teaching magnetic materials, the most effective approach is:
a) List all magnetic materials for students to memorize
b) Provide various objects and let students test which are attracted to magnets
c) Only use textbook examples
d) Show pictures of magnetic materials
Q15. A teacher demonstrates breaking a chocolate bar into pieces and explains that magnets behave similarly. This is an example of:
a) Rote learning
b) Analogy method
c) Lecture method
d) Textbook method
Answer Key with Explanations
Pedagogical Reflection for Teachers 🤔
Think-Pair-Share Activity:
Think: How would you explain to students why the north pole of a compass points north, even though opposite poles attract?
Pair: Discuss with a colleague how you would set up a "Magnetism Discovery Center" with activities for each section of this chapter.
Share: Design a 15-minute activity to teach the difference between magnetic and non-magnetic materials using everyday objects.
NCERT Textbook Linkages 📚
| Class | Chapter | Topic |
|---|---|---|
| Class 6 | Chapter 13 | Fun with Magnets |
| Class 10 | Chapter 13 | Magnetic Effects of Electric Current |
| Class 12 | Chapter 5 | Magnetism and Matter |
Chapter End Notes
Key Terminology Glossary
| Term | Definition |
|---|---|
| Magnet | Object that attracts iron and materials containing iron, nickel, or cobalt |
| Magnetic materials | Materials attracted to magnets (iron, nickel, cobalt, steel) |
| Non-magnetic materials | Materials not attracted to magnets (wood, plastic, copper, aluminum) |
| Natural magnet | Magnet found in nature (lodestone/magnetite) |
| Artificial magnet | Magnet made by humans |
| Permanent magnet | Magnet that retains magnetism for long time |
| Temporary magnet | Magnet that loses magnetism quickly |
| Magnetic pole | Region where magnetic force is strongest |
| North pole (N) | End of magnet that points north when freely suspended |
| South pole (S) | End of magnet that points south when freely suspended |
| Magnetic field | Region around magnet where magnetic force acts |
| Magnetic compass | Instrument using magnetized needle to find direction |
| Magnetic declination | Angle between true north and magnetic north |
| Curie temperature | Temperature above which material loses magnetism |
Quick Tips for PSTET Aspirants ⚡
✅ Memorize with Mnemonics:
Magnetic Elements: "Iron Never Comes" = Iron, Nickel, Cobalt
Pole Rule: "Like Leave, Unlike Unite" = Like repel, Unlike attract
Earth's Magnetic Poles: "North Seeks South" = Compass N points to Earth's magnetic S pole (near geographic N)
Magnet Making Methods: "Stroke Double Induce Electric" = Single-touch, Double-touch, Induction, Electrical
✅ Common Exam Traps:
Magnetite is the ONLY natural magnet—iron, nickel, cobalt are magnetic but not naturally occurring as magnets
Repulsion is the ONLY sure test—attraction can happen with magnetic materials
Broken magnets become COMPLETE magnets—never isolated poles
Earth's magnetic N pole is actually a SOUTH pole magnetically—this confuses many students
Geographic poles ≠ Magnetic poles—they are at different locations
✅ Important Facts:
Lodestone = magnetite (Fe₃O₄)
Curie temperature of iron: 770°C
Magnetic field strength: Earth ~0.5 Gauss; small bar magnet ~100 Gauss; neodymium magnet ~12,000 Gauss
Compass invented: China, ~1000 CE
Magnetic poles always in pairs
Last magnetic reversal: ~780,000 years ago
Answers to "Check Your Understanding"
[To be filled by student]
📝 Note for Self-Study: After completing this chapter, ensure you can:
Tell the story of how magnets were discovered
List 5 magnetic and 5 non-magnetic materials
Differentiate between natural and artificial magnets with examples
Explain the law of magnetic poles and demonstrate with examples
Describe what happens when you break a magnet
Explain how a compass works and how Earth's magnetism causes it
Describe three methods of making magnets
Explain the difference between permanent and temporary magnets
Describe Earth's magnetic field and its characteristics
