The short answer
One equation, v = fλ, behind light, sound, ripples and earthquakes — plus the traps that trip people up.
Written and checked by GAMSAT tutors — not AI-generated.
Try the reasoning style
We treat forgetting as a failure — a lapse to be patched with reminders and records. Yet a mind that kept everything could not think; it would drown in the undifferentiated noise of every moment it had ever lived. To forget is not so much to lose information as to decide, mostly without our noticing, what was never worth keeping.
The author's argument relies most directly on which unstated assumption?
Pick an option to see how the tutor reasons to the answer — not just whether you were right.
Not quite — the answer is B.
Work backwards from the conclusion: a mind that ‘kept everything’ supposedly ‘could not think.’ That only follows if thinking means leaving most of experience out — so B is the premise the argument quietly rests on. A raises reliability, which the passage never weighs; C contradicts ‘mostly without our noticing’; D smuggles in a claim about intellect the passage never makes. The question rewards finding the hidden premise, not recalling a fact.
Light, sound, ripples on a pond, earthquakes — all waves, all carrying energy without carrying matter along with them. Almost every wave question comes back to one equation: (speed = frequency × wavelength).
The one equation
. Frequency (Hz) is how many waves pass per second; wavelength is the length of one wave; period . The speed is set by the medium — so when a wave moves into a new medium, changes but stays the same, which forces to change.
Transverse vs longitudinal
Transverse
- Oscillation is perpendicular to travel
- Has crests and troughs
- Light, water surface, waves on a string
Longitudinal
- Oscillation is parallel to travel
- Has compressions and rarefactions
- Sound, a pushed slinky
Frequency is fixed by the source
When a wave crosses into a new medium (e.g. light entering glass), its frequency does not change — the source still wiggles at the same rate. The speed changes, so the wavelength changes to match. Many questions test exactly this.
Worked example
A sound wave travels at 340 m/s with a frequency of 170 Hz. What is its wavelength?
Check yourself
A wave passes into a medium where its speed halves, but the source's frequency is unchanged. What happens to the wavelength?
Key takeaways
- v = fλ ties speed, frequency and wavelength together.
- Period T = 1/f; amplitude relates to energy, not speed.
- Transverse: oscillation ⟂ travel (light). Longitudinal: oscillation ∥ travel (sound).
- Wave speed is set by the medium.
- Crossing media: frequency stays fixed; speed and wavelength change together.
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