Case study·Standard multi-step (3/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
A convex lens first forms a sharp image of an object needle on a screen. A convex mirror is then placed between the lens and that image, and the mirror is adjusted until the reflected image has no parallax with the object needle. The distance between the mirror and the first lens-image position is .
Total: 3 marks
(a) What does the no-parallax condition show in this method? (1 mark)
(b) Find the radius of curvature of the convex mirror. (1 mark)
(c) Find its focal length. (1 mark)
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