Science · Natural phenomena · chapter 10 of 13
Class 10 Science Chapter 10: The Human Eye and the Colourful World case study question with answers
One case-based question of the kind the board asks in Section E: a passage and a figure, then 3 parts worth 4 marks in all, with the answer and the marking scheme for each. Written from the NCERT chapter.
Case study · 4 marks
In the school laboratory at Kochi, Fatima fixes a triangular glass prism ABC on a sheet of white paper and traces its outline. She sends a narrow ray of light from a pin at P towards the face AB. The ray meets AB at E, travels inside the glass to F on the face AC and leaves along FS. She draws the normals at E and F, and extends the incident ray PE with a dashed line beyond the prism, as shown in the figure. She then measures the angles at E and F with a protractor.
Part 1 · 1 mark
In the figure, EF is the
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Answer: (b) refracted ray
PE is the incident ray, EF the refracted ray inside the glass and FS the emergent ray.
Part 2 · 1 mark
At E, compared with the normal drawn there, the ray
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Answer: (a) bends towards the normal
At E the ray passes from air into glass, so it bends towards the normal.
Part 3 · 2 marks
Name the angle between the dashed extension of PE and the emergent ray FS. Towards which part of the prism is the ray bent, and at which faces?
Answer and marking scheme
It is the angle of deviation. The ray is deviated towards the base BC of the prism, at both refracting faces, AB and AC.
- angle of deviation (1)
- towards the base, at both faces (1)
Or
Fatima replaces the pin and ray with a narrow beam of sunlight. Name what she sees on a screen beyond the face AC, and state which colour is bent the most and which the least.
Answer and marking scheme
A band of colours, the spectrum, formed by dispersion. Violet is bent the most and red the least.
- spectrum by dispersion (1)
- violet most, red least (1)
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