UPCAT Physics — Fluids, Waves & LightCheat Sheet
Cheat sheet for UPCAT Physics — Fluids, Waves & Light. Compact, printable, and organised around the concepts University of the Philippines tests most frequently in the UPCAT 2026. Perfect for the week before exam day.
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 - Cheat sheet
Your last-minute revision companion for mastering fluids, waves, and light concepts for UPCAT and other college entrance exams.
Sections
Formulas
Formula
v = λf
Meaning
v = wave speed (m/s), λ = wavelength (m), f = frequency (Hz)
Watch Out
Don't confuse frequency (Hz) with period (s) - they're reciprocals
When To Use
Finding any wave property when two others are known
Formula
T = 1/f
Meaning
T = period (s), f = frequency (Hz)
Watch Out
Period is in seconds, frequency is in Hertz (1/s)
When To Use
Converting between frequency and period
Formula
v_sound = 343 m/s (at 20°C in air)
Meaning
Speed of sound in air at room temperature
Watch Out
Speed changes with temperature and medium
When To Use
Sound wave problems unless other medium specified
Common Values
Value
3.0 × 10⁸ m/s
Symbol
c
Quantity
Speed of light in vacuum
Value
343 m/s
Symbol
v
Quantity
Speed of sound in air (20°C)
Section Title
Wave Properties & Formulas
Important Facts
- Energy carried by wave increases with amplitude squared
- All electromagnetic waves travel at 3.0 × 10⁸ m/s in vacuum
- Sound cannot travel through vacuum - needs medium
- Higher frequency = shorter wavelength (when speed is constant)
- Wave speed depends on medium properties, not frequency or wavelength
Key Definitions
Term
Wavelength
Example
Crest to crest or trough to trough
Definition
Distance between two consecutive points in phase on a wave
Term
Frequency
Example
60 Hz means 60 waves per second
Definition
Number of complete waves passing a point per second
Term
Amplitude
Example
Height of wave crest from center line
Definition
Maximum displacement from equilibrium position
Term
Transverse wave
Example
Light waves, waves on a string
Definition
Particles vibrate perpendicular to wave direction
Term
Longitudinal wave
Example
Sound waves, compression waves
Definition
Particles vibrate parallel to wave direction
Diagrams To Know
- Transverse wave showing wavelength, amplitude, crest, trough
- Longitudinal wave showing compressions and rarefactions
- Wave reflection at fixed and free ends
- Wave interference patterns (constructive and destructive)
Section Title
Wave Behaviors
Important Facts
- Reflection: angle of incidence = angle of reflection
- Refraction occurs due to change in wave speed
- Diffraction is more noticeable when opening size ≈ wavelength
- Interference requires coherent waves (same frequency)
- Doppler effect: frequency changes when source or observer moves
Key Definitions
Term
Reflection
Example
Echo from a wall
Definition
Wave bounces back when hitting a barrier
Term
Refraction
Example
Straw appears bent in water
Definition
Wave bends when entering different medium due to speed change
Term
Diffraction
Example
Sound heard around corners
Definition
Wave bends around obstacles or through openings
Term
Interference
Example
Noise-cancelling headphones use destructive interference
Definition
Waves combine when they meet
Term
Constructive interference
Example
Two speakers in phase create louder sound
Definition
Waves add up to make larger amplitude
Term
Destructive interference
Example
Waves 180° out of phase create silence
Definition
Waves cancel each other out
Diagrams To Know
- Wave reflection showing incident and reflected rays
- Wave refraction showing bending at interface
- Diffraction through single slit and around obstacles
- Interference pattern from two sources
Formulas
Formula
c = 3.0 × 10⁸ m/s
Meaning
Speed of light in vacuum
Watch Out
Speed is slower in any material medium
When To Use
All electromagnetic wave problems in vacuum
Common Values
Value
3.0 × 10⁸ m/s
Symbol
c
Quantity
Speed of light
Section Title
Light Properties
Important Facts
- Light is a form of energy that can do work
- We see objects when light from them enters our eyes
- Light waves are electromagnetic waves
- Color of object = color of light it emits or reflects
- White light contains all colors of visible spectrum
Key Definitions
Term
Luminous body
Example
Sun, light bulb, candle flame
Definition
Object that produces and emits its own light
Term
Illuminated body
Example
Moon, book, person
Definition
Object visible only when light from source strikes it
Term
Transparent
Example
Clear glass, clean water
Definition
Allows light to pass through clearly
Term
Translucent
Example
Frosted glass, tissue paper
Definition
Lets light pass through but distorts it
Term
Opaque
Example
Wood, metal, cardboard
Definition
Does not let light pass through at all
Term
Electromagnetic wave
Example
Light, radio waves, X-rays
Definition
Transverse wave of vibrating electric and magnetic fields
Diagrams To Know
- Electromagnetic spectrum showing all wave types
- Ray diagrams for reflection and refraction
- Light dispersion through prism
- Eye anatomy showing how we detect light
Formulas
Formula
Intensity ∝ (Amplitude)²
Meaning
Sound intensity proportional to amplitude squared
Watch Out
Doubling amplitude increases intensity by factor of 4
When To Use
Relating loudness to wave amplitude
Common Values
Value
20 Hz to 20,000 Hz
Symbol
f
Quantity
Human hearing range
Section Title
Sound Waves
Important Facts
- Sound needs medium to travel - no sound in vacuum
- Sound speed depends on medium temperature and density
- Higher temperature = faster sound speed
- Decibel scale is logarithmic, not linear
- Human hearing range: 20 Hz to 20,000 Hz
Key Definitions
Term
Sound wave
Example
Voice from vocal cords, music from speakers
Definition
Longitudinal wave produced by vibrating objects
Term
Intensity
Example
Measured in decibels (dB)
Definition
Amount of energy wave carries per second across unit area
Term
Loudness
Example
How loud something sounds to our ears
Definition
Human perception of sound intensity
Term
Pitch
Example
High pitch = high frequency, low pitch = low frequency
Definition
Human perception of sound frequency
Diagrams To Know
- Longitudinal wave showing compressions and rarefactions
- Sound wave frequency vs pitch relationship
- Decibel scale with common sound levels
Common Values
Value
400-700 nm
Symbol
λ
Quantity
Visible light wavelength range
Section Title
Electromagnetic Spectrum
Important Facts
- All EM waves travel at speed of light in vacuum
- Higher frequency = higher energy = shorter wavelength
- Sun emits mainly infrared, visible, and UV radiation
- Visible light is tiny portion of EM spectrum
- Order by increasing frequency: Radio → Infrared → Visible → UV → X-ray → Gamma
Key Definitions
Term
Radio waves
Example
AM/FM radio, TV broadcasts
Definition
Longest wavelength EM waves used for communication
Term
Infrared waves
Example
Remote controls, thermal imaging
Definition
Heat radiation, longer wavelength than visible light
Term
Visible light
Example
Colors from red (longest) to violet (shortest)
Definition
EM waves human eyes can detect
Term
Ultraviolet waves
Example
UV lamps, sterilization
Definition
Higher energy than visible light, can cause sunburn
Term
X-rays
Example
Medical imaging, airport security
Definition
High energy waves that penetrate soft tissue
Term
Gamma rays
Example
Nuclear reactions, cancer treatment
Definition
Highest energy EM waves
Diagrams To Know
- Complete electromagnetic spectrum with wavelengths
- Visible light spectrum (ROYGBIV)
- Energy levels of different EM waves
Must Remember
- v = λf is THE fundamental wave equation - memorize it
- Speed of light = 3.0 × 10⁸ m/s in vacuum
- Sound speed = 343 m/s in air at 20°C
- Light is electromagnetic wave - transverse, no medium needed
- Sound is longitudinal wave - needs medium, cannot travel in vacuum
- Luminous objects emit light, illuminated objects reflect light
- Higher frequency = shorter wavelength (when speed constant)
- Wave energy increases with amplitude squared
- EM spectrum order: Radio → IR → Visible → UV → X-ray → Gamma
- Angle of incidence = angle of reflection
Last Minute Tips
- For wave speed problems: always identify what you're given and what you need from v = λf
- Remember units: frequency in Hz, wavelength in meters, speed in m/s
- Sound problems: if no medium specified, assume air at room temperature (343 m/s)
- Light problems: if in vacuum or air, use c = 3.0 × 10⁸ m/s
- Wave behavior questions: reflection bounces back, refraction bends at interface, diffraction bends around obstacles
Comparison Tables
Rows
Values
- Perpendicular to wave direction
- Parallel to wave direction
Property
Particle motion
Values
- Light, radio waves, waves on string
- Sound, compression waves
Property
Examples
Values
- No (EM waves can travel in vacuum)
- Yes (needs material medium)
Property
Medium required
Values
- Crests and troughs
- Compressions and rarefactions
Property
Parts of wave
Columns
- Property
- Transverse
- Longitudinal
Table Title
Transverse vs Longitudinal Waves
Rows
Values
- Complete
- Partial
- None
Property
Light transmission
Values
- Clear
- Blurred/distorted
- Not visible
Property
Object visibility
Values
- Clear glass, air
- Frosted glass, thin cloth
- Wood, metal
Property
Examples
Columns
- Property
- Transparent
- Translucent
- Opaque
Table Title
Transparent vs Translucent vs Opaque
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