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 → Modern Physics → Radioactivity ↓


Half-life and radioactive decay


In the fascinating world of physics, especially when studying radioactivity, two important concepts often come up - half-life and radioactive decay. These concepts reveal the nature of how radioactive substances change over time and their properties that affect a wide range of scientific and practical applications.

What is radioactive decay?

At the core of radioactivity is the phenomenon known as radioactive decay. Radioactive decay is a natural process by which an unstable atomic nucleus loses energy by emitting radiation. Here, radiation refers to particles such as alpha particles, beta particles, and gamma rays. These emissions result in the transformation of the original (or parent) atom into a different (or daughter) atom.

Understanding radioactive decay with an example

Let's start with a simple hypothetical example. Imagine you have a radioactive element called element X. Over time, element X decays into another element, element Y, by emitting radiation. This is radioactive decay - where the identity of the element changes along with its nucleus.

// A simple illustration of radioactive decay: Start: Element X (Parent) ----------> Decay ----------> End: Element Y (Daughter) + Particles

Understanding half-life

The concept of half-life is closely linked to radioactive decay. Half-life is defined as the time it takes for half of the radioactive nuclei in a sample to decay. This rate constant provides a way to measure how quickly a radioactive substance decays into a non-radioactive form or how long it will remain active.

Half-life visualization

To understand the half-life, let's look at a visual example. Imagine we start with 100 units of radioactive material:

Starting: 100 units Half-life after 1: 50 units After 2 half-lives: 25 units After 3 half-lives: 12.5 units

Here, each bar represents the amount of substance at successive half-lives.

Mathematics of half-life

To determine the half-life mathematically we can use the formula:

N(t) = N₀ * (1/2)^(t/T)

Where:

  • N(t) = the amount of radioactive substance that remains after time t
  • N₀ = initial amount of substance
  • T = half life of the substance

Applications of half-life and radioactive decay

These concepts are not just theoretical; they have practical applications too:

1. Carbon dating

In archaeology, the half-life of carbon-14 (about 5,730 years) is used to accurately date archaeological and geological samples.

2. Medical use

Radioactive isotopes, such as technetium-99m, which have very short half-lives, are used in medical diagnostics, allowing imaging and tracking of physiological processes.

3. Nuclear energy

Given the long half-lives of some waste products, understanding radioactive decay is extremely important for managing nuclear reactors and disposing of nuclear waste.

Example: Carbon dating

Let us learn about carbon dating in detail. Living organisms constantly exchange carbon with the environment, and thus have the same level of C-14 as the environment around them. After death, the consumption of C-14 stops and decay begins.

// Carbon-14 decay representation over time: Living Organism (absorbing C-14) --------------> Death (stops absorbing C-14) ----------> Decay

By measuring the remaining C-14, scientists can estimate when the organism died. This process is known as radiocarbon dating.

Types of radioactive decay

There are several types of radioactive decay, each involving different particles:

1. Alpha decay

In alpha decay an alpha particle is released. The original element loses two protons and two neutrons, and changes into a new element.

Example of alpha decay

Consider the disintegration of uranium-238 into thorium-234:

// Alpha decay of Uranium-238: Uranium-238 --> Thorium-234 + alpha particle (2 protons + 2 neutrons)

2. Beta decay

Beta decay occurs when a neutron turns into a proton, emitting a beta particle (high energy electron).

Example of beta decay

An example of this is the disintegration of carbon-14 into nitrogen-14:

// Beta decay of Carbon-14: Carbon-14 --> Nitrogen-14 + beta particle

3. Gamma decay

Gamma decay emits extra energy as a gamma ray, without changing the number of protons or neutrons.

Safety measures and handling

Understanding these concepts helps to handle radioactive materials safely. Lead shields and monitoring devices are commonly used to protect against radiation exposure, especially in laboratories and medical settings.

Summary

In short, half-life and radioactive decay are crucial to understanding the behavior of radioactive materials. These processes have far-reaching implications and applications in science and technology, from dating ancient remains to medical diagnosis.


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Half-life and radioactive decay

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