Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Electricity and Magnetism → Magnetism ↓


Earth's magnetism


Earth's magnetism is a fascinating topic that explains not only how a compass works but also how our planet itself acts like a giant magnet. In this explainer, we'll explore various aspects of Earth's magnetism, including what causes it, how it's measured, and its effects on living creatures and technology. We'll keep the concepts simple and use visual and text examples to help you understand the topic thoroughly.

What is the magnetism of the earth?

Imagine a giant bar magnet inside the Earth. Although it's not exactly like a kitchen magnet, the Earth has a magnetic field that is produced primarily by electric currents in the liquid outer core. This magnetic field radiates out into space and interacts with solar winds. But before we get into the details of the Earth's magnetic field, let's start with some basic concepts of magnetism.

Basics of magnetism

Magnetism is an invisible force of attraction or repulsion that acts at a distance due to charged particles. Magnetism lies in the motion of electrons within atoms. Atoms contain electrons that spin and orbit around the nucleus, and the motion of these charged particles produces a magnetic field. If many electrons spin in the same direction, they create a strong magnetic field, making the material itself a magnet.

Visual example:

N S

This diagram shows a simple magnet with north and south poles. The lines represent the magnetic field created by the magnet.

Components of the Earth's magnetic field

The Earth's magnetism is mainly due to three factors:

  1. Core: Earth has a liquid outer core composed mainly of iron and nickel, which rotates around the solid inner core. This motion generates electric currents, which create magnetic fields.
  2. Self-sustaining dynamo: Caused by the rotation of the planets, these electric currents create a self-sustaining dynamo effect that maintains the Earth's magnetic field.
  3. Convection currents: Within the molten iron, convection currents also contribute to the motion needed to generate the Earth's magnetic field.

Visual example:

main

This diagram depicts the Earth, and emphasizes the activities at its core that produce the magnetic field.

Magnetic poles and magnetic declination

The Earth's magnetic poles are not exactly aligned with the geographic poles. This discrepancy is an important concept in navigation:

  • Magnetic north and south poles: These are the points where the Earth's magnetic field lines meet. They are not fixed and move due to changes in electric currents.
  • Geodetic north vs. magnetic north: On maps, we use geographic north, which is called true north. The angle between true north and magnetic north is known as magnetic declination.
Magnetic Declination = True North - Magnetic North

This formula helps sailors to correct their compass readings to know the correct direction.

Magnetosphere

The region around the Earth that is affected by its magnetic field is called the magnetosphere. This magnetic field forms a shield that protects the Earth from solar and cosmic radiation.

Visual example:

This view shows Earth's magnetic field, depicted as a protective layer around the planet.

The magnetosphere is very important because it deflects solar winds and cosmic particles, protecting life on Earth. Without it, radiation would destroy the atmosphere and life would become impossible.

Measuring the Earth's magnetic field

The Earth's magnetic field is measured by its direction and strength. Magnetic field strength is often measured in units called teslas (T).

  • Compass: A simple and ancient instrument used to find the direction of the earth's magnetic field. It aligns itself with the magnetic field lines.
  • Magnetometer: Advanced instruments used for accurate measurement of magnetic field intensity and direction.

Effects of Earth's magnetism

The Earth's magnetism affects a variety of phenomena and technology:

  1. Compass navigation: The compass needle aligns with the Earth's magnetic field, aiding in navigation throughout history.
  2. Auroras: These spectacular light displays, like the northern lights, occur when solar particles interact with magnetic fields.
  3. Animal navigation: Many animals, such as birds and sea turtles, use the Earth's magnetic field to navigate during migration.
  4. Technology interference: Magnetic storms caused by solar activity can interfere with satellite operations, GPS and communication systems.

Historical perspective on Earth's magnetism

Understanding of the Earth's magnetism has evolved over the centuries:

  • Ancient theory: Early cultures realized that the Earth has magnetic properties; they used loadstones for navigation.
  • 1600 AD: William Gilbert proposes that the Earth itself behaves like a giant magnet, explaining magnetic variations on the planet.
  • 19th century: The theory of geomagnetism advanced with the study of electric currents and their magnetic effects.

Fluctuations and reversals in the Earth's magnetic field

The Earth's magnetic field is dynamic, having changed its polarity many times in history. These reversals are recorded in geological materials and help scientists understand the Earth's internal processes.

  • Magnetic stripes: These stripes on the ocean floor show a pattern of polarity reversal. They are evidence of plate tectonics and sea floor spreading.
  • Geological time scale: Magnetic reversal data are used to date geological events and form part of the geological time scale.

Historical pattern:

past Present

This sequence shows magnetic reversals recorded in seafloor rocks, with each stripe representing a change in polarity.

Current research and future questions

Research on Earth's magnetic field continues, with scientists using satellites and probes to observe the dynamics of the magnetic field. Questions remain about the exact mechanisms within the core that drive the planet's magnetic properties, and the effects of future magnetic reversals on life and technology.

In conclusion, Earth's magnetism is a complex and important aspect of our planet, affecting navigation, protecting us from cosmic and solar radiation, and providing insight into geological processes. Understanding it not only helps us navigate, but also helps us appreciate the planet's complex systems.


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Earth's magnetism

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