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 ↓


Magnetic field and field lines


Magnetism is an essential aspect of physics that deals with the forces, fields, and effects produced by magnets. One of the key components of understanding magnetism is the concept of magnetic field and magnetic field lines. In this explanation, we will delve deeper into the concept of magnetic field, field lines, and their importance.

What is a magnetic field?

A magnetic field is an invisible force field that surrounds a magnetic object. It is responsible for exerting a magnetic force on other materials within the area. Magnetic fields are created by moving charges within the object or by electric current flowing through a wire.

In simple terms, a magnetic field is the region around a magnetic material or a moving electric charge within which the force of magnetism acts. The strength of this magnetic field varies with the distance from the source, it becomes much weaker as we move away from the magnet.

Magnetic field characteristics

  • They are vector fields - that is, they have both magnitude and direction.
  • They exert forces on moving charges and other magnets.
  • The direction of the magnetic field is indicated by the direction of the force applied to the positive test charge.

Magnetic field lines

Magnetic field lines are a visual representation of a magnetic field. These lines provide a way to see the direction and strength of a magnetic field. Some basic properties of magnetic field lines are as follows:

  • They emerge from the north pole of the magnet and enter the south pole.
  • They never bite each other.
  • The density of the field lines indicates the strength of the magnetic field. Closer lines indicate stronger fields.
  • They form a closed loop from north to south pole outside the magnet and back from south to north pole inside the magnet.

Visual examples of magnetic field lines

Field lines around a bar magnet:

N S

This diagram shows a simplified representation of the magnetic field lines around a bar magnet. Notice how the lines emerge from the north pole and bend toward the south pole.

Why do magnetic field lines never cross each other?

Magnetic field lines never cross each other because the magnetic field has a unique direction at any given point in space. If the field lines cross each other, it would mean that the magnetic field has two different directions at the same place, which is impossible.

How to visualize a magnetic field

There are some simple ways to visualize the magnetic field around a magnet:

Use of iron filings

One popular method is to sprinkle iron filings around a magnet on a piece of paper. These filings align with the magnetic field lines, visually representing the field around the magnet.

Use of magnetic compass

A magnetic compass can also be used to locate magnetic field lines. By placing the compass at different points around a magnet, you can see how the needle aligns with the field lines.

Mathematics and Magnetic Fields

In physics, magnetic fields are often expressed as mathematical equations. The most common formula relating to the magnetic field is:

B = μ₀ * (I / 2πr)

Where:

  • B is the magnetic field strength
  • μ₀ is the permittivity of free space
  • I am the present
  • r is the distance from the wire

Earth's magnetic field

The Earth itself behaves like a giant magnet. It has a magnetic field with magnetic force lines extending from magnetic north to magnetic south. This magnetic field plays an important role in navigation and is used by the compass in determining direction.

Visualization of the Earth's magnetic field:

N S

This diagram shows the Earth's magnetic field lines. Although in reality it is much more complicated, it helps to understand the basic concept of where the lines leave magnetic north and re-enter magnetic south.

Interaction with electric current

The relationship between electricity and magnetism is fundamental to electromagnetism. When electric current passes through a conductor, it produces a magnetic field around it. This is the principle behind electromagnets, which can be used in a variety of devices such as electric motors, relays, and transformers.

Right hand rule for current carrying wires:

A useful rule for determining the direction of the magnetic field around a current-carrying wire is the right-hand rule. If you wrap your right hand around the wire with your thumb in the direction of the current, your fingers will bend in the direction of the magnetic field.

Applications of Magnetic Fields

Magnetic fields have many applications in science and technology:

  • Magnetic resonance imaging (MRI): Used in medical diagnosis.
  • Electric motors and generators: convert electrical energy into mechanical energy and vice versa.
  • Compass: Use the Earth's magnetic field for navigation.
  • Data storage solutions: Magnetic fields in hard drives to store data.

Conclusion

Understanding magnetic fields and field lines is crucial to understanding how magnetism works and affects our world. From helping in navigation to enabling complex technological advancements, magnetic fields play a vital role in our daily lives. Following the simple concepts of field lines and visualizing them helps provide a clear understanding of how magnets interact with each other and with electric currents.


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Magnetic field and field lines

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