The short answer
Reflection, refraction and Snell's law — why light bends and which way.
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 bends when it changes speed. That one idea explains refraction, why a straw looks broken in water, lenses, and total internal reflection. Add the simple rule for reflection and you can handle most optics questions.
Reflection and refraction
Reflection: the angle of incidence equals the angle of reflection (measured from the normal). Refraction: light changes speed crossing into a new medium and bends, following Snell's law , where is the refractive index (higher = slower light).
Which way does it bend?
Going into a denser medium (higher , e.g. air → glass), light slows down and bends toward the normal. Going into a less dense medium (glass → air), it speeds up and bends away from the normal. Past a critical angle, none escapes — total internal reflection (how optical fibres work).
Worked example
A ray of light passes from air () into water (). Does it bend toward or away from the normal, and why?
Check yourself
Light passes from glass into air. Compared to glass, light in air travels faster, so the ray:
Key takeaways
- Reflection: angle of incidence = angle of reflection (from the normal).
- Refraction: light bends because its speed changes; Snell's law .
- Refractive index ; higher n = slower light.
- Into a denser medium → slows, bends TOWARD the normal (and vice versa).
- Beyond the critical angle → total internal reflection (optical fibres).
Practise this with real GAMSAT-style questions
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