What this covers
Within Waves, this standard is one students often meet in structured questions. A focused lesson turns "I understand it" into "I can score it".
How it is examined
It can appear in Paper 1 (objective) and Paper 2 (structured), and where an experiment applies, in Paper 3. We do not predict which questions appear; we prepare the technique for all of them.
A common mistake
How to study it
Learn the definition precisely, practise one or two SPM-style questions with full working, and link it to the rest of Waves. If it keeps costing marks, a one-to-one lesson fixes exactly that.
Waves · Formulas · Exam Papers
What you need to know
Refraction occurs when a wave passes from one medium into another in which its speed is different, causing the wave to change direction unless it travels along the normal. When a wave moves into a region where its speed decreases, such as water waves entering a shallower region, the wavelength decreases while the frequency stays exactly the same, since frequency depends only on the source producing the wave.
This can be understood using the wave equation v = fλ: because f is constant, a decrease in v must be accompanied by a proportional decrease in λ. The direction of travel bends toward the normal when the wave slows down, and bends away from the normal when the wave speeds up.
In a ripple tank, refraction is demonstrated by placing a glass plate under part of the water to create a shallower region; straight wavefronts crossing the boundary become more closely spaced and change direction in the shallow region. Diagrams must show the normal at the boundary, the wavefronts closer together in the slower, shallower region, and the direction of travel bending correctly toward the normal.
Worked example
In a ripple tank, water waves travel at a speed of 0.30 m s⁻¹ in the deep region with a wavelength of 0.03 m. Using v = fλ, the frequency of the source is found from f = v/λ = 0.30 m s⁻¹ / 0.03 m = 10 Hz.
When the same waves cross into a shallower region where the speed decreases to 0.20 m s⁻¹, the frequency stays constant at 10 Hz because it depends on the vibrating source, not the medium. The new wavelength in the shallow region is calculated by rearranging v = fλ to give λ = v/f = 0.20 m s⁻¹ / 10 Hz = 0.02 m.
This shows clearly that the wavelength decreases from 0.03 m to 0.02 m as the wave slows down, while the frequency of 10 Hz remains unchanged throughout. Students should present this as two separate steps: first finding frequency in the original medium, then using that unchanged frequency to find the new wavelength in the second medium, always showing the correct units at each stage.
How it is examined
Paper 1 questions test whether frequency, wavelength or speed changes during refraction, often through statements to be judged true or false, or direct calculation using v = fλ across two regions. Paper 2 structured questions frequently show a ripple tank diagram with a boundary between deep and shallow water and use command words such as "state" for what remains constant, "explain" for why wavelength changes while frequency does not, and "calculate" for finding an unknown speed or wavelength, each requiring units at every step of working.
"Explain" responses should reference the wave equation and the fact that frequency is fixed by the source. Paper 3 practical work commonly involves a ripple tank with a glass plate creating a shallow region, where students observe and sketch the change in wavefront spacing and direction as waves cross the boundary.
A common mistake is believing that frequency changes when a wave refracts, when in fact only speed and wavelength change; another is forgetting that bending is toward the normal when slowing down and away from the normal when speeding up.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)