Page 13 - 1202 Question Bank Physics Form 4

Section C
Answer all questions.

8. When light rays encounter curved surfaces between two media, images can be formed by either reflection
or refraction due to these surfaces. We can design mirrors and lenses to form images with desired
characteristics.
(a) Explain how does a curved surface change the direction of light? HOTS Applying [2 marks]
(b) Diagram 8.1 shows the design of an oven made by a student for boiling soup using solar energy.

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Diagram 8.1
You are required to suggest new design of an oven so that the soup in the pot boils in a shorter time. In
your explanation, emphasize on the following aspects:
(i) Size of the oven
(ii) Shape of the oven
(iii) Position of the pot
(iv) The type of surface for the oven
(v) The variation of the orientation for the oven with time HOTS Creating [10 marks]
(c) In Diagram 8.2, an object is placed in front of a converging lens at a distance equal to twice the focal
length f of the lens. On the other side of the lens is a concave mirror of focal length f separated from
1 2
the lens by a distance 2(f + f ). Light from the object passes rightward through the lens, reflects from
1 2
the mirror, passes leftward through the lens, and forms a final image of the object.
f f
1 2
O

2f 2(f + f )
1 1 2
Diagram 8.2

What are
(i) the distance between the lens and that final image,
(ii) the overall lateral magnification M of the object and
(iii) the characteristics of the final image? HOTS Evaluating [8 marks]

104 Question 8:
SOS TIP (c) First, the convex lens form a real image of the object, I at a distance 2f to the right of the lens. This is 2(f + f ) – 2f = 2f in front of the concave mirror. SOS TIP
1
1
2
1
1
2
The subsequent image formed by the concave mirror, I is located at a distance 2f to the left of the mirror. This is 2(f + f ) – 2f = 2f to the right of the
2
2
1
2
1
2
convex lens. The final image, I is formed at a distance 2f to the left of the lens. [You may construct a ray diagram to verify these]
3
1
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