An atom is the basic building block of all matter. Everything you see is made up of atoms!

• Protons: Positively charged particles found in the nucleus (center) of the atom.
• Neutrons: Neutral particles (no charge) also found in the nucleus.
• Electrons: Negatively charged particles that move in shells around the nucleus.
• Nucleus: The tiny, dense center of the atom, containing protons and neutrons.

The number of protons determines which element an atom is (for example, 1 proton = Hydrogen, 6 protons = Carbon).

Watch: Atomic Structure (Hindi)

Radioactive decay is the process where unstable atomic nuclei lose energy by emitting radiation. It changes one element into another.

• Alpha decay: Releases an alpha particle (2 protons, 2 neutrons).
• Beta decay: Releases a beta particle (electron or positron).
• Gamma decay: Releases energy as gamma rays (very strong).

Watch: Radioactivity & Types (Hindi)

Alpha (α): Heavy, slow, blocked by paper.
Beta (β): Lighter, can penetrate paper but not aluminum.
Gamma (γ): Energy ray, needs thick lead to block.

Watch: Types of Radiation (Hindi)

Exposure to high radiation can cause:

• Radiation burns
• Nausea, vomiting, hair loss
• Cancers (like leukemia, thyroid cancer)
• Genetic mutations

Protection: Limit time, increase distance, use shielding (lead, concrete), avoid radioactive sources.

Watch: Radiation Safety (Hindi)

Examples of radioactive elements:

• Uranium (U): Used in nuclear power & bombs.
• Thorium (Th): Used in some reactors.
• Radium (Ra): Used in old paints, very dangerous.
• Polonium (Po), Francium (Fr), Radon (Rn), Plutonium (Pu), Promethium (Pm), Actinium (Ac)

Watch: Radioactive Elements (Hindi)

Matter is anything that has mass and takes up space. It exists in five states: solid, liquid, gas, plasma, and Bose-Einstein condensate.

Watch: Matter (Hindi)

Pure Substances: Only one type of particle (elements or compounds).
Mixtures: Two or more substances mixed (air, soil, salt water).

Watch: Types of Matter (Hindi)

Frozen light is a state where light (photons) is almost stopped using special materials such as Bose-Einstein condensates. This has uses in quantum computing.

Watch: Bose-Einstein Condensate (Hindi)

Antimatter is made of particles that are the opposite of normal matter (e.g., positrons instead of electrons). When antimatter meets matter, both are destroyed and energy is released.

Watch: Antimatter (Hindi)

Dark matter is invisible matter that does not emit light but has gravity. It holds galaxies together and is one of the biggest mysteries in science.

Watch: Dark Matter (Hindi)

Magnetism is a force that pulls or pushes certain materials, like iron, cobalt, and nickel. Magnets have two poles: North and South.
Magnetic Force is the force exerted by magnets when they attract or repel each other. Opposite poles attract, and like poles repel.
Magnetic Field is the space around a magnet where magnetic force acts. You can see this with iron filings around a bar magnet.
Right-Hand Rule: Used to find the direction of the magnetic field around a current-carrying wire: Thumb points in the direction of current, curled fingers show the direction of the field.

Watch: Magnetism and Magnetic Force (Hindi)

Diamagnetic Substances: These are weakly repelled by a magnetic field. They do not retain magnetism after the external field is removed. Examples: bismuth, copper, water.
Paramagnetic Substances: These are weakly attracted by a magnetic field and do not retain magnetism after the external field is removed. Examples: aluminium, platinum.
Ferromagnetic Substances: These are strongly attracted by a magnetic field and can become permanent magnets. Examples: iron, cobalt, nickel.

Watch: Types of Magnetic Materials (Hindi)

Einstein's relativity has two parts:

• Special Relativity: The speed of light is the same for all observers. Time and space are not absolute. Famous equation: E = mc².
• General Relativity: Gravity is not a force but the curvature of spacetime. Massive objects like planets bend space and time around them.

Watch: Theory of Relativity (Hindi)

Gravity pulls everything towards everything else. It keeps us on Earth, makes the planets orbit the sun, and causes tides.

Watch: Gravity (Hindi)

The universe began as a tiny point and has been expanding ever since. This is called the Big Bang theory.

Watch: Big Bang (Hindi)