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 ↓


Natural and artificial magnets


Magnetism is a fascinating phenomenon that has fascinated humans for centuries. It is a force that can attract or repel objects without touching them. The study of magnets and their properties is an interesting part of the physics subject. In this detailed explanation, we will explore what magnets are, the difference between natural and artificial magnets, and many interesting aspects related to magnetism.

Understanding magnetism

Magnetism is a force that is caused by moving electric charges. It is a fundamental property of matter, associated with the movement of electrons in atoms. Every magnet has two poles, known as the north pole and the south pole. The magnetic force is the strongest at these poles.

The magnetic field is represented visually by lines of force that form loops around the magnet. These lines emerge from the north pole and enter the south pole. The field lines never cross each other, and the density of these lines indicates the strength of the magnetic field. The closer the lines are, the stronger the magnetic field.

Natural magnets

Natural magnets are magnets that occur naturally in the environment. They are typically composed of minerals that have magnetic properties. The most common type of natural magnet is lodestone, a form of magnetite (Fe₃O₄). These magnets were used by ancient sailors as primitive compasses due to their ability to point to magnetic north.

Lodestone (Magnetite): Fe₃O₄

The main characteristics of natural magnets are as follows:

  • Origin: Naturally found in the earth.
  • Durability: Retains its magnetic properties for a long time.
  • Strength: Their magnetic field is generally weak compared to artificial magnets.

Artificial magnets

Artificial magnets, also known as man-made magnets, are created by inducing magnetic properties in certain materials. These magnets can be made permanent or temporary, and they are designed to have specific magnetic properties depending on their intended use.

There are many types of artificial magnets, including:

  1. Temporary magnets: These are magnets that exhibit magnetic properties only in the presence of a magnetic field. A common example is an electromagnet, which is a coil of wire that acts like a magnet when an electric current flows through it.
  2. Permanent magnets: These retain their magnetic properties even after the external magnetic field is removed. Common materials used for permanent magnets include iron, cobalt, nickel, and alloys such as neodymium-iron-boron (NdFeB).
    3. Neodymium Iron Boron (NdFeB): Strongest type of permanent magnet
  3. Electromagnet: A magnetic field is produced by wrapping a wire into a coil and passing an electric current through the coil. The strength of the electromagnet can be adjusted by changing the current flowing through the wire.

Difference between natural and artificial magnets

There are several major differences between natural and artificial magnets. These differences affect their applications and utility in various fields. Some of these differences are as follows:

Natural magnets Artificial magnets
It is found in nature. Manufactured by manual processes.
Usually weak magnetic force. Can be made with controlled power.
Unknown geometry and shape. Manufactured in specific shapes and sizes.
Only permanent. Can be permanent or temporary.

Magnetic properties and uses

Understanding the differences and characteristics of natural and artificial magnets allows for a wide variety of applications. Here are some examples:

  • Navigation: Magnetism is used in compasses for navigation. The compass needle is a thin magnet balanced on a point to rotate freely and always points to magnetic north.
  • Industrial uses: Magnets are used in a variety of industrial processes, such as separating magnetic materials from non-magnetic materials and lifting heavy iron or steel objects using cranes equipped with large electromagnets.
  • Electronics: Many electronic devices, such as speakers, microphones, hard drives, and motors, rely on magnetism to function.
  • Medical uses: Techniques such as magnetic resonance imaging (MRI) use powerful magnets and radio waves to make images of organs and tissues inside the body.
    • MRI: Magnetic Resonance Imaging uses powerful magnets

Magnetic domains

The concept of magnetic domains is important to understanding how substances are magnetized. A magnetic domain is a region within a substance where the magnetic fields of atoms are grouped together and aligned in the same direction. In non-magnetic substances, these domains are oriented randomly, eliminating the magnetic effects.

When a material becomes magnetized, these domains become aligned in the same direction, producing a net magnetic effect. The more aligned the domains are, the stronger the magnetic field.

Making artificial magnets

There are a few methods used to create artificial magnets, and they usually involve aligning the magnetic domains in a material. Here are some methods:

  • Stroking: A magnetic material can be magnetized by rubbing it repeatedly in one direction with a natural magnet. This method aligns the magnetic domains in the metal.
  • Electrical method: By passing an electric current around or through a magnetic material using a coil of wire, the material can be magnetized. This technique is used to make electromagnets.

Magnetic field visualization example

To understand magnetism it is necessary to look at magnetic fields. Below is an example depiction of the magnetic field lines around a bar magnet:

N S Magnetic field lines around a bar magnet with north (N) and south (S) poles.

Conclusion

Magnets are an essential part of the physical world and have many practical applications in science and technology. Understanding the difference between natural and artificial magnets provides insight into their various uses. While natural magnets such as lodestones have historical significance, artificial magnets provide versatile and powerful alternatives for modern applications. Whether in the form of permanent magnets, electromagnets or industrial magnets, their impact can be seen far and wide. The study of magnetism remains a dynamic and exciting field in physics, full of opportunities for discovery and innovation.


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Natural and artificial magnets

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