Science

🔦 Light

Properties

• Travels in straight lines → explains shadows.

• Speed: ~300,000 km/s in a vacuum.

• Transverse wave (vibrations perpendicular to travel).

• Can travel through a vacuum, unlike sound.

Reflection

• Law of Reflection: angle of incidence = angle of reflection.

• Smooth surfaces (mirrors) reflect clearly; rough surfaces scatter.

• Used in periscopes, telescopes, car headlights.

Refraction

• Light bends when passing between materials of different densities.

• Toward the normal in denser media, away in less dense.

• Explains “bent straw” effect in water.

• Lenses use refraction to focus light.

Dispersion & Colour

• White light splits into a rainbow through a prism.

• Colours = different wavelengths (red long, violet short).

• Filters absorb some wavelengths, transmit others.

Vision – Basic Parts of the Eye

• Cornea → clear front surface, bends light to start focusing.

• Pupil → dark opening, controls how much light enters.

• Iris → coloured ring of muscle, adjusts pupil size.

• Lens → flexible structure, fine-tunes focus onto retina.

• Retina → light-sensitive layer at the back, contains rods (brightness) and cones (colour).

• Optic Nerve → carries signals from retina to brain.

Process: Light enters through cornea → passes pupil (controlled by iris) → focused by lens → lands on retina → signals travel via optic nerve → brain interprets image.

Everyday Connections

• Sunsets look red due to scattering.

• Diamonds sparkle from multiple refractions.

• Fibre optics use total internal reflection to carry internet signals.

🔊 Sound

Nature

• Longitudinal wave: particles vibrate back and forth in the same direction.

• Needs a medium (air, water, solids).

• Cannot travel in space.

Speed

• Fastest in solids, slower in liquids, slowest in gases.

• ~343 m/s in air at room temperature.

• Example: thunder heard after lightning.

Frequency, Pitch, Wavelength, Hertz, Decibels

• Frequency: number of vibrations per second (measured in Hz).

• Pitch: how high or low a sound seems; linked to frequency.

• Wavelength: distance between compressions; short wavelength = high frequency.

• Hertz (Hz): unit of frequency (1 Hz = 1 vibration per second).

• Decibels (dB): unit of loudness; whisper ≈ 30 dB, conversation ≈ 60 dB, concert ≈ 120 dB.

Pitch & Loudness

• Pitch = frequency (high frequency = high pitch).

• Loudness = amplitude (large vibrations = louder).

• Human hearing range: ~20 Hz to 20,000 Hz.

Reflection of Sound

• Echoes when sound reflects off surfaces.

• Used in sonar, bats’ echolocation, ultrasound scans.

Applications

• Ultrasound in medicine and industry.

• Noise-cancelling headphones use interference.

• Seismology studies earthquakes with sound waves.

• Architecture designs auditoriums to control echoes.

Hearing

• Outer ear collects sound.

• Middle ear amplifies vibrations.

• Inner ear (cochlea) detects frequencies.

• Signals sent to brain via auditory nerve.

Everyday Connections

• Voices echo in halls.

• Soundproof rooms absorb waves.

• Music sounds richer indoors than outdoors.

📘 Big Picture – Light vs Sound