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Science 3% exam weight

High-yield pointers for CAT MCQs

Part of the UAE University CAT study roadmap. Science topic scienc-009 of Science.

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High-yield pointers for CAT MCQs

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Topic 9 of the UAE University CAT Science paper covers Waves, Sound, and Light at a Year 12–13 foundation level. The single most-tested relationship is the wave equation:

v = fλ, where v = wave speed (m/s), f = frequency (Hz), λ = wavelength (m).

Frequency stays locked to the source; speed and wavelength change when a wave enters a new medium. Sound is a longitudinal pressure wave needing matter, while light is a transverse electromagnetic wave travelling at 3 × 10⁸ m/s in vacuum.

PropertyTransverse waveLongitudinal wave
Vibration directionPerpendicular to propagationParallel to propagation
ExampleLight, waves on a stringSound, compression in a spring

High-yield pointers for CAT MCQs:

  • Refraction obeys Snell’s law: n₁ sin θ₁ = n₂ sin θ₂.
  • Total internal reflection only occurs going from a denser to a less dense medium.
  • A 10 dB rise equals a 10× intensity jump, not 10× loudness.

🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Wave fundamentals

A wave transfers energy through oscillation of particles or fields, without transporting matter. Two families exist. Transverse waves (light, ripples, a vibrating string) oscillate at right angles to the direction of travel, so they possess both crests and troughs. Longitudinal waves (sound, seismic P-waves) oscillate along the travel direction, producing alternating compressions and rarefactions.

The period T in seconds and frequency f in hertz are reciprocals: T = 1/f. Combine this with v = fλ to solve any one unknown when two of the others are given. Always convert kHz → Hz (×10³) and nm → m (×10⁻⁹) before substituting.

Sound and intensity

Sound travels faster in solids than liquids than gases because particle spacing affects how quickly the pressure pulse propagates. Loudness on the decibel scale follows β = 10 log(I/I₀), with reference intensity I₀ = 10⁻¹² W/m². Because the scale is logarithmic, doubling the sound intensity adds only about 3 dB.

Reflection and refraction

The laws of reflection demand that the angle of incidence equals the angle of reflection, with incident ray, reflected ray, and normal all in the same plane. For refraction, Snell’s law (n₁ sin θ₁ = n₂ sin θ₂) governs how a light ray bends at an interface. Entering a denser medium (higher n) bends the ray toward the normal.

CaseBehaviour at interface
Light → denser mediumBends toward normal, slows down
Light → less dense mediumBends away from normal, speeds up
Angle > critical angle (denser → less dense)Total internal reflection

Typical CAT question patterns

Expect 1-mark MCQs on unit-converted v = fλ calculations, a Snell’s law numerical with θ₁ unknown, and a one-line conceptual item asking whether sound can travel through vacuum, whether frequency changes between media, or which EM wave has the highest frequency.

🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Electromagnetic spectrum connections

Visible light occupies a narrow band between roughly 380 nm (violet) and 750 nm (red) within the electromagnetic spectrum. Order from low to high frequency: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Energy of a photon scales with frequency through E = hf (h = 6.63 × 10⁻³⁴ J·s), so gamma rays ionise atoms while radio waves merely warm tissues. CAT occasionally tests this ordering in reverse wavelength order.

Worked Snell’s law example

Light strikes a glass surface (n = 1.50) from air (n = 1.00) at θ₁ = 30°. Apply n₁ sin θ₁ = n₂ sin θ₂ → sin θ₂ = (1.00 × sin 30°)/1.50 = 0.333 → θ₂ ≈ 19.5°. Reverse the scenario to find the critical angle for glass-to-air: sin θc = 1.00/1.50 = 0.667 → θc ≈ 41.8°. Any incident angle above 41.8° from inside the glass produces total internal reflection — the basis of optical fibres.

Common mistakes and traps

  • Swapping θ₁ and θ₂ in Snell’s law, which often still yields a numerical answer but is physically wrong.
  • Treating dB as linear: a 20 dB rise is 100× intensity, not 20×.
  • Claiming light “speeds up” entering glass — it actually slows.
  • Drawing reflection diagrams without arrowheads, losing the 1-mark in trace-the-ray questions.

Exam strategy

With only 3% weight, spend roughly 3–4 minutes per question. Memorise v = fλ and Snell’s law in their exact symbolic form, practise two or three numerical drills with unit conversions, and move on. The Science section rewards breadth, not depth on any single topic.

Practice prompts

  1. A sound wave of frequency 440 Hz travels through air at 352 m/s. Find its wavelength and the new wavelength when it enters water where speed rises to 1480 m/s. (Answer: 0.80 m in air; frequency stays 440 Hz, wavelength becomes 3.36 m.)
  2. A ray hits a water–air boundary from inside water (n = 1.33) at 50°. Does it refract or undergo total internal reflection? (Answer: sin θc = 1/1.33 = 0.752, θc ≈ 48.8°, so 50° > θc — total internal reflection occurs.)

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