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 ↓


Properties of magnets


In the fascinating world of physics, magnets have always been a subject of curiosity and study. Magnets have unique properties that are not only important for understanding how they work but also help in their application in various technological advancements. In this guide, we will explore the fundamental properties of magnets, the science behind magnetism, and how these essential elements work in the broader realm of electricity and magnetism.

Introduction to magnetism

Magnetism refers to the force by which substances exert attractive or repulsive forces on other substances. This force is primarily observed in materials known as magnets. The cause of magnetism is the motion of electrons within an atom. When most of the electrons align their motion or spin in the same direction, they create a magnetic field.

Magnets come in different forms, such as bar magnets, ring magnets, disc magnets, and more. Regardless of their shape, all magnets exhibit certain properties. First, let's understand what a magnetic field looks like.

Magnetic field

The magnetic field is an invisible area around a magnet where the force of magnetism is dominant. The magnetic field is usually represented by field lines that emerge from the north pole and enter the south pole. This creates a visual representation of how magnets can affect objects within this field.

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The strength and direction of the magnetic field depend on the type and size of the magnet. Magnetic fields exert a force on other magnets and magnetic materials, such as iron filings, causing them to line up along the field lines.

Important properties of magnets

Magnets have certain properties that determine how they interact with their surroundings. These properties include polarity, magnetic fields, attraction and repulsion, and strength.

Difference of opinion

Every magnet has two poles: a north pole and a south pole. This is due to the directional flow of electrons within the magnet. The poles are where the magnetic force is the greatest.

Law of Magnetism: Like poles repel each other, while opposite poles attract each other.

For example, if you bring two north poles of different magnets together, they will repel each other. On the other hand, if you bring a north pole and a south pole together, they will attract each other.

Magnetic field

The magnetic field of a magnet refers to the space around the magnet within which the force of magnetism acts. This field is strongest at the poles and decreases as you move away from the source.

A practical example is how a compass works. The compass needle is essentially a tiny magnet that aligns itself in the north-south direction by responding to the Earth's magnetic field. This principle is used to determine direction in navigation.

Attraction and repulsion

As explained earlier, magnets exhibit attraction and repulsion. This characteristic is used in practical applications, such as maglev trains. Magnetic levitation (maglev) trains float above tracks using powerful magnets, eliminating friction and allowing for smooth and fast movement.

The formula to calculate the force between two magnets is:

F = (μ * (m1 * m2))/(4 * π * r^2)

Where:

  • F = force between the magnets
  • μ = permittivity of the medium
  • m1 and m2 = magnetic moments of the two magnets
  • r = distance between the centres of the two magnets

Magnetic strength

The strength of a magnet can be determined by the number of field lines it produces and the intensity of its magnetic field. The greater the number of lines and their density, the stronger the magnet.

Magnetic power is essential in industrial applications, such as metal sorting, in MRI machines in the medical field, and in electric motors and generators. Let's see how this works in practice.

Visualization of magnetic properties

A great way to look at the properties of magnets is to use a simple black box experiment, in which a magnet is moved under steel filings or small iron particles. This experiment helps us to see the magnetic field lines clearly.

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By placing a magnet beneath a sheet of paper and sprinkling iron filings over it, the filings align with the magnetic field lines, showing a clear pattern of magnetic effect. The filings collect at the ends of the magnet, showing the concentration of force at the poles.

Practical applications and daily life examples

Magnets are not only important in understanding physical laws, but they also have practical uses in everyday life. Here are some examples:

Electric motors and generators

Electric motors convert electrical energy into mechanical energy. This conversion is possible due to the interaction between magnetic fields and electric current. A typical example of this is a fan, where the motor rotates when electricity passes through the coil, moving the blades and creating air flow.

Data storage

Hard disks store data magnetically. They use read/write heads that convert digital data into magnetic patterns on the surface of the disk. The coating on the disk is a thin film that records data by changing its magnetic orientation to represent binary data.

Speakers and microphones

Speakers convert electrical signals into sound waves using magnets. The electrical audio signal passes through a coil of wire, producing a magnetic field that interacts with a permanent magnet. This interaction causes vibrations, which ultimately produce sound waves.

MRI machines

In medical imaging, MRI machines use powerful magnets to temporarily align hydrogen atoms in the body. This alignment, when disrupted by radio waves, produces signals that are used to create detailed images of organs and tissues.

Fridge magnets

A simple but everyday example of the use of magnets is refrigerator magnets, which stick to the metal surface of refrigerator doors using the principle of magnetic attraction. These useful objects often help to keep notes and reminders.

Understanding the earth's magnetism

The Earth itself is a giant magnet with its own magnetic field, which is why compasses work. The magnetic North Pole is not perfectly aligned with the geographic North Pole. Scientists believe that the movement of molten iron and nickel in the Earth's outer core creates electric currents, which in turn create the Earth's magnetic field.

Conclusion

Understanding magnets and their properties is essential to understanding broader concepts of physics, particularly electricity and magnetism. Magnets have fascinating properties such as polarity, attractive and repelling forces, and the creation of magnetic fields. These properties are responsible for many applications in technology and industry, making magnets indispensable in our modern world.


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Properties of magnets

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