. Practical physics. roduced by a closedC organ pipe ? Chapter XVIII. 1. If the opaque body in Fig. 382 is moved nearerto the screen ef, how does the penumbra change ? 2. The diameter of the moon is 2000 mi., that of the sun 860,000 mi.,and the sun is 93,000,000 mi. away. What is the length of the moonsxmibra ? 3. If the distance from the center of the earth to the center of themoon were exactly equal to the length of the moons umbra, over howwide a strip on the earths surface would the sun be totally eclipsed atany one time? 4. Look at the reflected image of an electric-light filament in apie
. Practical physics. roduced by a closedC organ pipe ? Chapter XVIII. 1. If the opaque body in Fig. 382 is moved nearerto the screen ef, how does the penumbra change ? 2. The diameter of the moon is 2000 mi., that of the sun 860,000 mi.,and the sun is 93,000,000 mi. away. What is the length of the moonsxmibra ? 3. If the distance from the center of the earth to the center of themoon were exactly equal to the length of the moons umbra, over howwide a strip on the earths surface would the sun be totally eclipsed atany one time? 4. Look at the reflected image of an electric-light filament in apiece of red glass. Why are there two images, one red and one white ? 5. Show by a diagram and explanation what is meant by critical angle. 6. The vertical diameter of the sun appears noticeably less than itshorizontal diameter just liefore rising and just before setting because ofrefraction due to the earths atmosphere. Explain. 7. In what direction must a fish look in orderto see the setting sun ? (See Fig. ) ~^-. FiG. 485. To an eye under water all exter-nal objects appear to lie within a cone whoseangle is 97° Fig. 480. Prismglass 8. Fig. 486 represents a section of a plate of prism glass. Explain whyglass of this sort is so much more efficient than ordinary window glass inilluminating the rears of dark stores on the ground floor in narrow streets. 9. In which medium, water or air, does light travel the faster?Give reasons for your answer. 10. Does a man above the surface of water appear to a fish below itfarther from or nearer to the surface than he actually is? Make anexplanatory wave diagram. QUESTIONS AND PROBLEMS 463 11. How far from a screen must a 4-candle-power light be placed togive the same illumination as a 16-candle-power electric light 3 m. away ? 12- If two plane surfaces placed 1 m. and 2 m. respectively from agiven light receive perpendicularly the same quantity of light, how musttheir areas compare ? State the law involved. 13. If two foot-candles are de
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectphysics, bookyear1922
