UPCAT Physics — Fluids, Waves & LightStudy Notes
Thorough study notes for Fluids, Waves & Light — the fastest path from zero to ready for UPCAT Physics. Structured for self-study reviewers who cannot attend a review centre, these notes cover the full concept library plus the UPCAT-specific twists University of the Philippines adds to its questions.
Exam context
On the UPCAT 2026, the Physics subtest carries a "Core" weight in University of the Philippines's pattern. Fluids, Waves & Light lands at position 5th out of 6 in the standard review order. Target score is UPG ≤ 2.2 typical, and roughly 20 items come from Physics on a typical UPCAT paper.
Fluids, Waves & Light - Study notes
This chapter explores three fundamental areas of physics that affect our daily lives: fluids (liquids and gases), waves (including sound), and light. Understanding these concepts helps explain everything from how we hear sounds to why objects appear different colors. These topics are essential for the UPCAT and other college entrance exams in the Philippines.
Summary
This chapter covers the fundamental physics of waves, sound, and light. Key concepts include the wave equation v = λf, wave behaviors (reflection, refraction, diffraction, interference), sound as compressional waves, and light as electromagnetic radiation traveling at 3.0 × 10⁸ m/s. Understanding how objects interact with light (transparent, translucent, opaque) and how we perceive color through our visual system is essential. These concepts explain everyday phenomena and are frequently tested in entrance exams.
Sections
Waves are disturbances that transfer energy without transferring matter. Think of waves in water - the water itself doesn't move forward, but the wave energy travels across the surface. There are two main types of waves: transverse waves (particles move perpendicular to wave direction, like guitar strings) and compressional waves (particles move parallel to wave direction, like sound waves). The fundamental wave equation v = λf connects three key properties: velocity (v), wavelength (λ), and frequency (f). This equation is crucial for solving wave problems in exams.
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Wave Properties and Fundamentals
Examples
- Guitar strings vibrating create transverse waves
- Sound waves are compressional waves in air
- Radio waves are electromagnetic waves traveling at light speed
- Example calculation: Sound wave with frequency 34 Hz and wavelength 10.0 m has speed v = (10.0)(34) = 340 m/s
Key Points
- Waves transport energy without transporting matter
- Transverse waves: particles move perpendicular to wave direction
- Compressional waves: particles move parallel to wave direction
- Wave equation: v = λf (velocity = wavelength × frequency)
- Wave energy increases with amplitude
Waves exhibit four important behaviors that explain many natural phenomena. Reflection occurs when waves bounce back after hitting a barrier - like echoes in caves or seeing your reflection in water. Refraction happens when waves change direction as they pass from one medium to another due to speed changes - this explains why a pencil looks bent in water. Diffraction allows waves to bend around obstacles and travel around corners - why you can hear someone calling from around a corner. Interference occurs when two or more waves meet and combine, creating patterns of reinforcement and cancellation.
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Wave Behaviors and Phenomena
Examples
- Echo in mountains (reflection)
- Pencil appearing bent in water (refraction)
- Hearing sounds around corners (diffraction)
- Noise-canceling headphones use destructive interference
Key Points
- Reflection: waves bounce back from barriers
- Refraction: waves change direction when changing mediums
- Diffraction: waves bend around obstacles and corners
- Interference: waves combine when they meet
- These behaviors explain many everyday phenomena
Sound waves are compressional waves created by vibrating objects. The speed of sound depends on the medium and temperature - it travels faster in solids than in gases. At room temperature, sound travels at approximately 340 m/s in air. Loudness relates to wave intensity (energy per unit area per second), measured in decibels. Pitch corresponds to frequency - higher frequency means higher pitch. The human ear can typically hear frequencies from 20 Hz to 20,000 Hz. Understanding sound is important for acoustics, music, and medical applications like ultrasound.
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Sound Waves
Examples
- Thunder sound traveling slower than lightning flash
- Tuning fork creating specific frequencies
- Ultrasound used in medical imaging
- Different musical instruments producing different pitches
Key Points
- Sound waves are compressional waves produced by vibrations
- Sound speed depends on medium and temperature
- Loudness relates to wave intensity (measured in decibels)
- Pitch relates to frequency
- Human hearing range: 20 Hz to 20,000 Hz
Light is electromagnetic energy that travels at 3.0 × 10⁸ m/s (300,000 km/s) in vacuum. Light exhibits wave properties and is part of the electromagnetic spectrum, which includes radio waves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Objects can be luminous (produce their own light, like the sun) or illuminated (reflect light from other sources, like the moon). Materials interact differently with light: transparent materials allow light to pass through clearly, translucent materials let light through but distort it, and opaque materials block light completely.
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Light and Electromagnetic Waves
Examples
- Sun is luminous, moon is illuminated
- Glass windows are transparent
- Frosted glass is translucent
- Wooden doors are opaque
- Radio waves, visible light, and X-rays are all electromagnetic
Key Points
- Light speed: 3.0 × 10⁸ m/s in vacuum
- Light is part of the electromagnetic spectrum
- Luminous objects produce their own light
- Illuminated objects reflect light from other sources
- Materials can be transparent, translucent, or opaque
Color is determined by the wavelength of light that reaches our eyes. Objects appear colored because they absorb some wavelengths and reflect others - the reflected wavelengths determine the color we see. White light contains all visible wavelengths, while black represents the absence of light. Our eyes contain specialized cells: rod cells detect light intensity (for night vision) and cone cells detect color. The retina converts light signals into electrical impulses that the brain interprets as images. This process explains how we perceive the colorful world around us.
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Color and Vision
Examples
- Red apple reflects red wavelengths, absorbs others
- Prism separating white light into rainbow colors
- Rod cells help us see in dim light
- Color blindness occurs when cone cells don't function properly
- Sunset appears red because atmosphere scatters blue light away
Key Points
- Color depends on wavelength of light
- Objects reflect some wavelengths and absorb others
- White light contains all visible wavelengths
- Rod cells detect light intensity, cone cells detect color
- Brain interprets electrical signals from retina as images
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