CBSE Class 10 Science 2026: question 35

Hints

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Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

1. (a) Ray diagram: Draw a triangular glass prism $PQR$. A ray $EF$ strikes face $PQ$ at $F$ and bends towards the normal $N_1{N}_1^{\prime }$ (air → glass), travelling as $FG$ inside the prism. At face $PR$ it emerges along $GH$, bending away from the normal $N_2{N}_2^{\prime }$ (glass → air). Arrows show the direction of light. Produce the incident ray $EF$ forward and the emergent ray $GH$ backward (dotted) so that they meet.

   1 mark

2. Labelling: mark angle of incidence $\angle i$ between $EF$ and $N_1{N}_1^{\prime }$, **angle of refraction $\angle r$** between $FG$ and the normal inside the prism, and angle of emergence $\angle e$ at $G$.

   ½ mark

3. Mark the **angle of deviation $\angle D$** as the angle between the produced incident ray and the emergent ray.

   ½ mark

4. (b) The angle of deviation does not change.

   ½ mark

5. Reason: by the principle of reversibility of light, the reversed ray follows exactly the same path backwards; the emergent ray becomes the incident ray, so $\angle e$ and $\angle i$ interchange and the ray retraces its original path, giving the same deviation.

   ½ mark

Answer: (a) Labelled prism diagram with $\angle r$ and $\angle D$ marked; (b) angle of deviation remains the same, as the ray retraces its path.

Revise the chapter

• Chapter: Light – Reflection and Refraction (notes, formulas, where marks are lost and every past question)