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Chapter 5: Q4DQ (page 1151)
Explain why the focal length of a plane mirror is infinite, and explain what it means for the focal point to be at infinity.
The focal length of a plane mirror is because the parallel rays couldn鈥檛 be focused hence f is infinity.
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The laws of optics also apply to electromagnetic waves invisible to the eye. A satellite TV dish is used to detect radio waves coming from orbiting satellites. Why is a curved reflecting surface (a 鈥渄ish鈥�) used? The dish is always concave, never convex; why? The actual radio receiver is placed on an arm and suspended in front of the dish. How far in front of the dish should it be placed?
A lensmaker wants to make a magnifying glass from glass that has an index of refraction n = 1.55 and a focal length of 20.0 cm. If the two surfaces of the lens are to have equal radii, what should that radius be?
A beam of light goes from one material into another. On physical grounds, explain why the wavelength changes but the frequency and period do not.
The cornea behaves as a thin lens of focal length approximately1.8 cm, although this varies a bit. The material of which it is made has an index of refraction of 1.38 cm , and its front surface is convex, with a radius of curvature of 5.0 mm. (a) If this focal length is in air, what is the radius of curvature of the back side of the cornea? (b) The closest distance at which a typical person can focus on an object (called the near point) is about 25cm, although this varies considerably with age. Where would the cornea focus the image of an 8.00 mm -tall object at the near point? (c) What is the height of the image in part (b)? Is this image real or virtual? Is it erect or inverted? (Note:The results obtained here are not strictly accurate because, on one side, the cornea has a fluid with a refractive index different from that of air.)
The eyepiece of a refracting telescope (see Fig. 34.53) has a focal length of 9.00 cm. The distance between objective and eyepiece is 1.20 m, and the final image is at infinity. What is the angular magnification of the telescope?
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