Long answer·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
In a concave-lens experiment using an auxiliary convex lens, the point where rays would have met without the concave lens is to the right of the concave lens. After the concave lens is introduced, the final real image is to its right.
Total: 4 marks
(a) State the sign of object distance for the concave lens in this setup. (1 mark)
(b) Use the lens formula to find the focal length. (2 marks)
(c) Why is the sign of focal length physically reasonable? (1 mark)
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