10/6/25
What is Potential Energy?
Potential energy is the stored energy an object has because of its position or condition.
It means the object has the potential to do work later — like move, fall, or cause something to happen.
Types (simple examples):
Gravitational potential energy
Stored in objects that are high up.
Example: A rock on a cliff, or a book on a shelf.
The higher it is, the more energy it has.
Elastic potential energy
Stored in stretched or compressed objects.
Example: A stretched rubber band or a compressed spring.
Chemical potential energy
Stored in chemicals like fuel, food, or batteries.
Released during chemical reactions.
Gravitational Potential Energy Formula:
GPE=mgh\text{GPE} = mghGPE=mgh
Where:
m = mass (kg)
g = gravitational field strength (usually 9.8 N/kg)
h = height (m)
What is Kinetic Energy?
Kinetic energy is the energy an object has because it is moving.
The faster or heavier the object, the more kinetic energy it has.
Simple Examples:
A moving car
A thrown ball
A person running
A falling apple
If it’s moving, it has kinetic energy.
If the object stops, kinetic energy = 0
If the object moves faster, kinetic energy increases a lot (because speed is squared)
1. Energies that come under Potential Energy (stored energy):
These are energies stored due to position, condition, or structure:
Gravitational potential energy → due to height
Elastic potential energy → in stretched/compressed objects (like springs, rubber bands)
Chemical energy → stored in chemical bonds (like food, fuel, batteries)
Nuclear energy → stored in the nucleus of atoms
Electrical potential energy → stored when charges are separated (like in capacitors)
2. Energies that come under Kinetic Energy (moving energy):
These are energies in motion or action:
Mechanical kinetic energy → moving objects (cars, balls, people)
Thermal (heat) energy → movement of particles in matter
Sound energy → energy from vibrating objects
Electrical kinetic energy → when charges are actually flowing (in a current)
Light (radiant) energy → movement of electromagnetic waves (like sunlight, X-rays)
3. Energies that don’t exactly fit only into kinetic or potential:
Some forms of energy involve both or are special cases:
Thermal energy → it's kinetic at particle level, but often treated separately
Electromagnetic energy → includes both electric & magnetic components, often as waves
Internal energy → total of kinetic + potential energy at particle level (used in thermodynamics)
THE END
11/06/2025
What is Heat?
Heat is just energy that moves from something hotter to something cooler. but - like... what is it actually?
Heat = movement of particles
The faster the particles move → the hotter the object
What is Temperature?
Temperature is a measure of how fast the particles in something are moving.
Particles (atoms, molecules) are always moving
The faster they move → the hotter the thing feels
The slower they move → the colder it is
What is Celsius?
Celsius (°C) is a temperature scale used to measure how hot or cold something is.
Quick examples:
Ice cube: 0°C
Room temp: ~25°C
Hot tea: ~70°C
Boiling water: 100°C
Oven: 180–220°C
Human body: 37°C
What is Specific Heat Capacity?
It’s the amount of heat energy needed to raise the temperature of 1 kg of a substance by 1°C
Q=mcΔT = formula
Where:
Q = heat energy (in joules, J)
m = mass (in kg)
c = specific heat capacity (J/kg°C)
ΔT = change in temperature (°C)
Refraction and Refraction index
What does the refractive index actually mean?
It tells you how much a material slows down light compared to the speed of light in a vacuum.
A higher refractive index = light bends more + moves slower
A lower refractive index = light bends less + moves faster
Two ways in which energy pases through a metal :-
1. Conduction by free electrons (main way)
Metals have free-moving electrons (called delocalized electrons)
When metal is heated, these electrons gain energy and move faster
They zoom around and transfer energy from hot areas to cold areas
2. Vibration of metal ions (atoms)
Metal atoms are arranged in a regular pattern (lattice)
When heated, atoms vibrate more
These vibrations pass to neighboring atoms, spreading the energy
THE END
12/6/25
what is refractive index ?
What does it mean?
When light moves from air into glass or water, it slows down and bends.
The refractive index (n) is a number that shows how much slower light travels in that material compared to a vacuum.
Formula :-
n= speed of light in vaccum / speed of light in material
What is Focal Length?
Focal length is the distance between the center of a lens or mirror and its focus point — the point where light rays meet (converge or appear to diverge) after passing through the lens or bouncing off the mirror.
In simple terms:
It tells you how strongly a lens or mirror bends light
Short focal length = bends light a lot
Long focal length = bends light a little
For a convex lens (converging):
Parallel light rays come in
They bend inward and meet at the focus point
Distance from lens to focus = focal length
For a concave lens (diverging):
Light rays spread out
But if you trace them backward, they seem to come from a focus
That imaginary point is the focus, and distance = focal length
THE END
