TE Enriched Sample (E)

Lighting 1 34 13. HKDSE 2012 Below is a diagram of a room, the illuminance at corner P is E under the illumination of a point light source S as shown. Neglect the reflections from the room surfaces. room S P Q θ The illuminance at point Q midway between P and S is A. 2 cos E i . B. 2 E cos i . C. 4 E . D. 8 E . 14. HKDSE 2013 LED usually produces monochromatic light because A. the difference in energy levels of the p-layer and n-layer in an LED is fixed. B. its surface is coated with only one type of fluorescent material. C. the operating temperature of an LED is fixed. D. current is only allowed to flow through an LED in one direction. 15. HKDSE 2013 Assume that 1000 W m −2 of solar power reaches a certain place vertically on the Earth’s surface. What is the power delivered to a solar panel of width 2 m and length 10 m inclined at 20° to the horizontal at that place? 10 m horizontal 20° 2 m A. 6840 W B. 7280 W C. 18 800 W D. 20 000 W 16. HKDSE 2014 For monochromatic light sources, which of the following pairs appear(s) to be equally bright to our eyes? (1) 1 lumen of red light and 1 lumen of green light (2) red light of l watt and green light of 1 watt (3) red light of 1 watt and 1 lumen of red light A. (1) only B. (3) only C. (1) and (2) only D. (2) and (3) only Structured Questions 17. The photo is a close-up view of an incandescent lamp. X (a) (i) Name X and suggest a suitable material for making it. (2 marks) (ii) What is the relation between the thickness of X and the rated power of the lamp? (1 mark) (b) Consider a new incandescent bulb. (i) During operation, the two ends of X that connect to the leads are cooler than the middle part. Briefly explain. [Hint: Lead is a good heat conductor.] (1 mark) (ii) After being used for several hundred hours, the middle part of X becomes thinner. Why? (1 mark) (iii) The thinner part gets thinner at a higher rate. Briefly explain. (2 marks) (c) An incandescent lamp now works from a 220 V mains. The stable current is 0.3 A. (i) What is the rated power of the bulb? (1 mark) (ii) In the first few milliseconds, the rms value of the current keeps changing. Is it increasing or decreasing? Why? (2 marks) C (78%) (11%) (1.3) Q3.3 A (28%) (55%) (1.2) Q3.1 C (54%) (26%) (1.3) Q3.2 (1.2) A (21%) (53%) (1.2) Q3.1 Filament, tungsten Decreasing 66 W Sample © United Prime Educational Publishing (HK) Limited, Pearson Education Asia Limited 2023 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publishers.