Victory for the ACT Student Text 15e

L ESSON 2 | R ESEARCH S UMMARY • 317 29 . The student discovered that the scale was not calibrated properly (set to zero) before it was used in Part 2. Which of the following is the simplest way to correct this mistake? A. Determine how much mass was added to the measurements from not zeroing the scale and subtract this value from entry 5 in Table 2. B. Determine how much mass was added to the measurements from not zeroing the scale and subtract this value from entries 3 and 5 in Table 2. C. Determine how much mass was added to the measurements from not zeroing the scale and subtract this value from entries 1, 2, and 5 and recalculate entries 3 and 5 in Table 2 D. No correction is necessary because any added mass from not zeroing the balance would cancel out in the calculations leading to entries 3 and 5.

28. Based on the information provided, decreasing the amount of salt in a salt- water solution will cause the freezing point of the solution to: F. increase only. G. decrease only. H. decrease, then increase. J. remain the same.

PASSAGE VI A useful property of lenses is their ability to form images of objects due to the refraction of light as it passes from one medium to another. Focal length is the distance between the center of a lens and the point at which a clear image of a very distant object is formed. If the object and image sizes are h and h’ ǡ ”‡•’‡…–‹˜‡Ž›ǡ –Š‡ ƒ‰‹ϐ‹…ƒ–‹‘ ‘ˆ –Š‡ Ž‡• ‹• –Š‡ ”ƒ–‹‘ ‘ˆ –Š‡ ‹ƒ‰‡ •‹œ‡ –‘ object size, or: ' h h o i = − (Equation 1) In Equation 1, o represents the distance between the center of the lens and the object and i ”‡’”‡•‡–• –Š‡ †‹•–ƒ…‡ „‡–™‡‡ –Š‡…‡–‡” ‘ˆ –Š‡ Ž‡• ƒ† –Š‡ ‹ƒ‰‡Ǥ Š‡ ƒ‰‹ϐ‹…ƒ–‹‘ ‹• represented as a negative number to indicate that an inverted image has a negative height and an upright image has a positive height. Experiment 1 A student places an LED candle 100 centimeters from a thin converging lens. A paper screen on the other side of the lens is moved until a sharply focused image of the candle light appears on the screen (Figure 1). The image distance and height are measured. The candle is moved 20 centimeters closer to the lens and the experiment repeated until an object distance of ʹͲ…‡–‹‡–‡”• ‹• ”‡ƒ…Š‡†Ǥ ‘” ‡ƒ…Š †ƒ–ƒ •‡–ǡ –Š‡ ƒ‰‹ϐ‹…ƒ–‹‘ ‹•…ƒŽ…—Žƒ–‡† ȋ ƒ„Ž‡ ͳȌǤ Table 1 Object Distance, o (cm) Image Distance, i (cm) Image Height, h’ (cm) 0DJQLÀFDWLRQ 100.0 11.1 –0.55 –0.11 80.0 11.4 –0.71 –0.14 60.0 12.0 –1.00 –0.20 40.0 13.3 –1.66 –0.33 20.0 20.0 –5.00 –1.00