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


Radioactivity, a fundamental concept in modern physics, refers to the process by which unstable atomic nuclei release energy in the form of radiation. This radiation may take the form of alpha particles, beta particles, or gamma rays. A deeper understanding of radioactivity provides insight into the forces and principles that govern the atomic nucleus and provides a gateway to exploring the nature of matter.

Origin of radioactivity

An atom consists of a nucleus made up of protons and neutrons, surrounded by electrons. The stability of an atomic nucleus depends on its ratio of protons and neutrons. When this delicate balance is disrupted, the nucleus becomes unstable, leading to a spontaneous change called radioactive decay. During this process, the unstable nucleus emits radiation to reach a more stable state.

Types of radioactive decay

Alpha decay

Alpha decay occurs when a nucleus emits an alpha particle, which is made up of 2 protons and 2 neutrons. This particle is essentially a helium nucleus. As a result, the original atom loses two protons and two neutrons, forming a new element that is lighter by four atomic mass units.

        Example: 
        ( _{92}^{238}text{U} rightarrow _{90}^{234}text{Th} + _2^4text{He} )

Alpha particles are relatively large and can be easily blocked by a sheet of paper or even skin. However, they can be harmful if swallowed or inhaled.

Beta decay

Beta decay involves the transformation of a neutron into a proton or vice versa. There are two types of beta decay: beta-minus (β-) decay and beta-plus (β+) decay.

Beta-minus decay

In beta-minus decay, a neutron is converted into a proton, and an electron (beta particle) and an antineutrino are emitted.

        Example:
        ( _6^{14}text{C} rightarrow _7^{14}text{N} + beta^- + overline{nu}_e )

Beta-plus decay

Beta-plus decay occurs when a proton converts into a neutron, releasing a positron and a neutrino.

        Example:
        ( _{11}^{22}text{Na} rightarrow _{10}^{22}text{Ne} + beta^+ + nu_e )

Beta particles are smaller than alpha particles and can penetrate deeper, but they can be stopped by a few millimeters of aluminum.

Gamma decay

Gamma decay occurs when an excited nucleus releases excess energy in the form of a gamma ray, which is a high-energy photon. It often occurs after other types of decay when the daughter nucleus is in an excited state.

        Example: 
        ( ^{60}text{Co*} rightarrow ^{60}text{Co} + gamma )

Gamma rays are extremely penetrating and require a dense material such as lead or several centimetres of concrete to stop them.

Understanding half-life

An essential concept of radioactivity is the half-life, which is the time it takes for half of the radioactive nuclei in a sample to decay. Understanding the half-life helps determine the age of ancient artifacts and the time frame of radioactive emissions.

        Formula:
        ,
        n(t) = n_0 left(frac{1}{2}right)^{frac{t}{T_{1/2}}}
        ,

Where,

  • N(t) = amount of substance remaining after time t
  • N_0 = initial amount of substance
  • T_{1/2} = half-life period

Imagine you have a 10-gram sample of a radioactive element with a half-life of 5 years. After 5 years, only 5 grams will remain. After another 5 years (10 years total), only 2.5 grams will remain, and so on.

Radioactivity in nature and industry

Radioactivity is a natural part of our environment. Elements such as uranium, thorium and radon are naturally radioactive. Small amounts of these and other radioactive elements are present in the Earth's crust.

In industry, radioactivity is used in a variety of applications. Nuclear power plants generate electricity using the energy from radioactive decay. Medical imaging and cancer treatments can involve radioactive isotopes, benefiting thousands of patients worldwide.

Safety and risks of radioactivity

While radioactivity has practical uses, it can also pose health risks. Ionizing radiation from radioactive decay can damage living tissue. Prolonged or intense exposure can increase the risk of radiation sickness, burns or cancer.

To minimize exposure, industries follow strict safety guidelines. Radiation exposure is monitored through devices such as Geiger counters, film badges, and dosimeters. Lead shielding and thick walls limit exposure, protecting workers and the general public.

Radioactivity and nuclear reactions

Nuclear reactions such as fission and fusion involve changes in the nucleus of an atom. Fission is the process of splitting a heavy nucleus into two lighter nuclei, releasing energy and neutrons. This process powers nuclear reactors and some types of weapons.

        Example of Fragmentation:
        (_{92}^{235}text{U} + text{n} rightarrow _{56}^{141}text{Ba} + _{36}^{92}text{Kr} + 3n + text{Energy})

Fusion combines lighter nuclei to form heavier nuclei, releasing energy. This powers the Sun and has the potential to be a source of energy in the future.

        Example of fusion:
        ( _1^2 text{H} + _1^3 text{H} rightarrow _2^4 text{He} + text{n} + text{Energy} )

Conclusion

Radioactivity is a remarkable phenomenon that connects the microscopic world of subatomic particles to everyday applications in health, industry, and energy. By understanding radioactivity and nuclear reactions, we can harness the profound forces at the heart of the atom, contributing to advances in science and technology while prioritizing safety and sustainability.


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Rutherford and Bohr model
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Radioactivity

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