Page 421 - Schaum's Outline of Theory and Problems of Applied Physics

406 LENSES [CHAP. 32

32.11. If the image of an object 6 cm from a lens is 6 cm behind the object, the lens has a focal length of
(a) −12 cm (c) +4cm
(b) +3cm (d) +12 cm

32.12. A candle 6 cm high is 80 cm in front of a lens whose focal length is +60 cm. The image is
(a) 2 cm high, erect (c) 18 cm high, erect
(b) 2 cm high, inverted (d) 18 cm high, inverted
32.13. A candle 6 cm high is 120 cm in front of a lens whose focal length is +60 cm. The image is
(a) 3 cm high, erect (c) 6 cm high, erect
(b) 3 cm high, inverted (d) 6 cm high, inverted

32.14. A candle 6 cm high is 150 cm in front of a lens whose focal length is +60 cm. The image is
(a) 4 cm long, erect (c) 9 cm long, erect
(b) 4 cm long, inverted (d) 9 cm long, inverted

32.15. The focal length of a magnifying glass that produces an image six times larger than an object 10 mm away is
(a) +1.4mm (c) +8.6mm
(b) +2.0mm (d) +12 mm

32.16. A projector whose lens has a focal length of +12 cm forms an image 90 cm high of a slide whose picture area is
30 mm high. How far is the lens from the screen?

(a) 348 cm (c) 372 cm
(b) 360 cm (d) 384 cm

Supplementary Problems

32.1. Does an air bubble in a tank of water converge or diverge light that passes through it?

32.2. (a) Can a diverging lens ever form an inverted image of a real object? (b) Can a converging lens?
32.3. (a) Can a diverging lens ever form a real image of a real object? (b) Can a converging lens ever form a virtual image
of a real object?
32.4. If the screen is moved closer to a movie projector, how should the projector’s lens be moved to restore the image to
a sharp focus?
32.5. A double-convex lens has surfaces whose radii are both 50 cm. The index of refraction of the glass is 1.52. Find the
focal length of the lens.

32.6. A meniscus lens has a concave surface of radius 30 cm and a convex surface of radius 25 cm. The index of refraction
of the glass is 1.50. (a) Find the focal length of the lens. (b) Is it a converging or a diverging lens?

32.7. A planoconcave lens has one plane surface and one concave surface. If a planoconcave lens of focal length −10 cm
is to be ground from optical glass of index of refraction 1.50, find the radius of curvature of the concave surface.

32.8. Glycerin has an index of refraction of 1.47. Find the focal length in glycerin of a lens made of flint glass (n = 1.63)
whose focal length in air is +10 cm.

32.9. Find the index of refraction of the glass used in a planoconvex lens of focal length 12 cm whose convex surface has
a radius of 7 cm.