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


Magnetism is a fascinating aspect of physics that describes the force exerted by magnets when they attract or repel each other. It is connected to electricity and is part of a larger framework known as the electromagnetic force. This concept plays a vital role in a variety of technologies and is important in the natural world, affecting everything from navigation systems to animal migration.

Introduction to magnets

Magnets are objects that produce a magnetic field, which is invisible to the human eye, but can be seen as lines of force emanating from the north to the south poles. There are natural magnets, such as loadstones, and artificial magnets, such as those made from iron or nickel alloys.

Example: When you stick a magnet on your fridge, it is because the fridge door is usually made of metal, and the magnet tries to stick due to the attraction between opposite poles.

Properties of magnets

Magnets have many interesting properties:

  • Poles: Every magnet has two poles, a north pole and a south pole. Like poles repel each other, while opposite poles attract each other.
  • Magnetic field: The space around a magnet within which its force is effective is called the magnetic field. This field is represented as lines extending from the north pole to the south pole.
  • Attraction and repulsion: Magnets can attract ferromagnetic materials such as iron, nickel, and cobalt.

The magnetic field is depicted in the figure given below.

N S

In the diagram above, the magnetic field lines go from the north (N) pole to the south (S) pole, showing the direction of the magnetic field. The poles are represented by the two circular ends of the magnet.

Magnetic materials

Materials may be classified based on their magnetic properties:

  • Ferromagnetic: strongly attracted to magnets. Example, iron, nickel, cobalt.
  • Paramagnetic: poorly attracted by magnetic fields. Example, aluminum, platinum.
  • Diamagnetic: Slightly repelled by magnets. Example, copper, gold.
Example: Paper clips are made of steel, which is ferromagnetic. Therefore, they are easily attracted by a magnet.

Earth's magnetism

The Earth itself acts like a giant magnet, with its magnetic field extending from its center to where it meets the solar wind. This is important in the study of magnetism because it shows us that magnetic forces work on very large scales.

N S S N

The diagram shows the Earth's magnetic poles, with magnetic field lines running from near the North Pole to the South Pole. This is why a compass, which is a tiny magnet, points north.

Electromagnetism

Electromagnetism is the branch of physics that involves the study of the electromagnetic force, a type of physical interaction between electrically charged particles. The electromagnetic force is carried by electromagnetic fields made up of electric fields and magnetic fields.

When electric current passes through a wire, a magnetic field is generated around it. This phenomenon is described by Ampere's law, which states that the magnetic field in the space around an electric current is proportional to the electric current that is its source.

B = (µ₀ * I) / (2 * π * r)

In this formula, B is the magnetic field, µ₀ is the permeability of free space, I is the current, and r is the distance from the wire.

Example: Winding a wire into a coil and passing an electric current through it creates an electromagnet. This is the basis of devices such as electric bells, cranes for lifting scrap metal, and magnetic recording.

Magnetic effect of electric current

This effect is used in electromagnets, a type of magnet in which a magnetic field is generated by an electric current. Electromagnets are widely used in various electrical devices such as motors, generators, relays, and hard disks.

Electricity N S

The diagram shows a simple electromagnet made by coiling a coil of wire and passing an electric current through it. A soft iron core within the coil greatly enhances the magnetism, as shown by the concentrated force lines around the electromagnet.

Real life applications of magnetism

Magnetism has many real-world applications:

  • Medical equipment: MRI machines use magnetic fields to take pictures of the inside of the human body.
  • Data storage: Hard drives use a magnetic coating to store data.
  • Transportation: Maglev trains hover above tracks using powerful magnetic fields, which reduce friction.
Example: At home, magnets are often used to keep a closet door latch closed. The magnetic strip pulls a small metal rod mounted on the door, preventing the door from opening.

Conclusion

To understand magnetism, it is important to understand the forces exerted by magnets, the effect of materials on these forces, and how electricity can produce magnetic effects. This knowledge is very important as it forms the basis of various technological innovations and natural phenomena that show the interrelationship between electricity and magnetism.


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Magnetism

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