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Physics Form 4 Answers

• Focal length of mirror Q = 10 cm. (b) The eyepiece is used to
Object is located at radius of observe the image formed
curvature, image distance = 2f. by the second prism.
• Therefore, the mirror Q has a 45° 45° (ii)
shorter focal length. 45° 45° Right-angle prism
SPM Practice 6 Distant
object at
Objective Questions the back
1. B 2. C 3. B 4. C 5. B 45° Cylindrical
6. C 7. C 8. C 9. D 10. D 45° tube
11. C 12. A 13. B 14. B 15. C 45°
16. A 17. C 18. A 19. A 20. C
21. C 22. D 23. D 24. B 25. C
45° 45° An inverted
Subjective Questions 45° image Right-angle prism
Section A (c) (i) When the prism at the
Glass top periscope is laterally
1. (a) inverted, it can be used to
Air observe the object behind
Total internal the observer over an
Light ray reflection occurs here obstacle. In this case, the
image seen is inverted
A light ray is transmitted (iii) • A right-angle prism uses
(b) (i) f = 10 cm, u = 12 cm through a curved fibre optic total internal reflection
1 1 1 1 1 1 that occurs a series of total to reflect light. The light
f = + → 10 = 12 + v internal reflections on the reflected by the prism
u
v
1 1 1 6 – 5 1 inner surface. surface is 100%.
v = 10 – 12 = 60 = 60 (ii) • Fiber optic cables are • Image formed by right-
v = 60 cm lighter and thinner. angle prism is sharper.
Therefore, distance between • Transmission of signal
the screen and the object with almost no energy
= u + v = 12 + 60 = 72 cm loss along the optical PRE-SP M MODEL P APER
PRE-SPM MODEL PAPER
v 60 fiber.
(ii) m = = = 5 (d) (i)
u 12 Objective Questions
(c) The minimum height of the Right-angle
screen = 24 × 5 prism 1. B 2. B 3. C 4. A 5. D
= 120 cm 6. B 7. C 8. A 9. B 10. C
(d) If the distance between the lens 11. A 12. A 13. B 14. A 15. A
and the image = 10 cm = f, then Distant object Cylindrical 16. B 17. C 18. A 19. D 20. C
object is at the focal point and tube 21. B 22. A 23. C 24. A 25. B
image formed is virtual and at 26. C 27. D 28. A 29. D 30. A
infinity. Therefore, image cannot 31. C 32. C 33. A 34. D 35. C
be seen on the screen. 36. D 37. A 38. D 39. D 40. D
41. C 42. B 43. A 44. B 45. B
Image at infinity 46. B 47. D 48. C 49. C 50. C
Upright image
Right-angle Subjective Questions
prism
F F Section A
• A periscope is build using 1. (a) • time / length
two right-angle prisms • velocity / force
arrange in an cylindrical (b) (i) acceleration
Section B tube as shown in the (ii) the original length of the
2. (a) (i) The critical angle of glass is diagram above. spring
42° which means that if the • The prism acts like a
angle of incidence in glass perfect mirror when light 2. (a) Initially, there is no air resistance
(denser medium) is 42°, ray hits the inner surface acted on the skydiver. Therefore,
then the angle of refraction of the prism at an angle the skydiver experience a free
in the air is 90°. greater than 42°. The first fall due to gravitational force.
(ii) Total internal reflection prism turns the image (b) When the parachute is opened,
the air resistance acting on the
1 from a distant object 90°,
(iii) sin c = n and then the second parachute is greater than the
1 prism turns the image weight of the skydiver. The net
n = force acting on the parachute
sin c back to upright. upward causes upward
1
= sin 42 • Object lens is placed in acceleration.
front of the first prism on
= 1.49 top to find a distant object.
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ANS FOC PHYSICF F4 1P.indd 263 29/01/2020 2:04 PM