Light
What Is Light?
Light is a form of energy called electromagnetic radiation.
It’s produced by luminous objects (like the Sun or a lightbulb).
Light travels in a straight line.
Light waves are transverse waves (a wave where the movement goes up and down, but the wave travels forward.
Features of a Light Wave
Term | Definition |
Amplitude | How tall the wave is — from the middle to the peak. |
Frequency | How many waves pass per second (measured in Hz). |
Wavelength | Distance between two wave peaks (in meters). |
Vacuum | A space with no particles — light moves fastest here. |
Speed of Light | 300,000 km per second in a vacuum. |
Energy Transfer | Light carries energy from one place to another. |
Particle-Free Movement | Light doesn’t need a medium — unlike sound. |
Light in Different Materials
Transparent: All light goes through (e.g. clear glass).
Translucent: Some light goes through (e.g. frosted glass).
Opaque: No light goes through (e.g. wood).
🟥 Scattering happens when light bounces off particles in all directions.
🟨 Absorption is when light is taken in and converted to heat.
🟩 Reflection is light bouncing back from a surface.
Light bounces off shiny or smooth surfaces.
Incident ray: The light coming in.
Reflected ray: The light bouncing out.
Normal line: Drawn at 90° to the surface.
📐 Law of Reflection:
Angle of incidence = Angle of reflection
Refraction
Light bends when it moves between materials like air and glass.
It slows down when entering denser materials and speeds up when leaving them.
🧪 A straw in a glass of water looks bent because light is refracted.
How We See – The Eye
Eye Part | What It Does |
Retina | Detects light and forms an image. |
Pupil | Hole where light enters. |
Lens | Focuses light onto the retina. |
Optic Nerve | Sends signals to your brain. |
Think of the eye like a camera:
Lens focuses the image
Retina is the film/sensor
Optic nerve is the cable to the brain
How the Eye Sees
The human eye sees when light enters through the pupil — the hole in the middle of the iris. This light then passes through the lens, which bends (refracts) the light to focus it onto the retina at the back of the eye. The retina contains special cells that detect light and convert it into electrical signals. These signals are sent to the brain through the optic nerve, allowing us to see an image.
Top Tips:
⚡ Light is a form of energy
⚡ Light doesn’t need particles to travel — it even moves through a vacuum! That's why we can see the Sun from space.
⚡ Use this trick: A-F-W → Amplitude, Frequency, Wavelength. All three describe wave shapes and speed!
⚡ If you can't see through it clearly, it’s not transparent — it's either translucent or opaque.
⚡ Draw diagrams neatly and always label the normal line first — it’s your reference point for measuring angles!