Chapter 11.pdf

Example Problem 11.11A camera with a 200-mm lens makes a real image of a bird on film.The film is located 201 mm behind the lens. Determine thedistance from the lens to the bird.GivenFocal length of lens, f = 200 mmImage distance, d i= 201 mmRequiredObject distance of the bird from the lens, d oAnalysis and Solution1 1 1Use the thin lens formula:d+ =od if1 1 1 1Rearrange the formula ford: = od of d iSubstitute the values and their units, and solve the problem.1 1 1d= of d i1 1 1 1d= o 200 201 mm1 2.4876 10 –5d=ommTake the reciprocal of both sides of the equation to eliminate thefractions.d o= 4.02 10 4 mmParaphraseThe bird is about 40.2 m away from the camera lens.Practice Problems1. A convex lens with afocal length of 18 mmproduces an image 25 mmfrom the lens. Howfar from the lens is theobject?2. Where is the object placedif a convex lens with afocal length of 7.00 cmproduces a virtual image3.00 cm from the lens?3. An image of a candle isproduced by a convexlens 14 cm away. If thefocal length of the lens is7.0 cm, how far from thelens is the candle placed?D22STSEScience, Technology, Society, and the EnvironmentTwo-Way MirrorsA two-way mirror is partly reflective and partlytransparent. The reflective coating of a two-way mirroris not nearly as thick on a regular mirror so that somelight gets reflected and some passes through. For themirror to work properly, there must be a significantdifference in the brightness of light on the two sides.The side where the observers are positioned must bedark so that no light goes through the mirror to theother room. The other side, where the person beingobserved is located, must be bright so that enough ofthe light is reflected and the person does not seethrough to the other side.1. How might you be able to tell if you were lookingat a two-way mirror, without looking at it from theother side?2. Two-way mirrors are sometimes used in traininghospitals so interns can watch operations beingperformed. Brainstorm other situations in whichtwo-way mirrors would be useful.3. What issues do you think arise from the use oftwo-way mirrors?Ray diagrams model the behaviour of light in mirrors and lenses.457