4. A concave mirror has a of focal length 25 cm. If an object is placed 75 cm fr

Question

4. A concave mirror has a of focal length 25 cm. If an object is placed 75 cm from the mirror, where is the image? A) 25 cm B) 37.5 cm C) 50 cm D) 00 cm E) 150 cm 5. A converging lens with a focal length of 15 cm produces a real image three times the size of the real object. Where is the object? A) d, 10 cm B) d, 5 cm C) d, 20 cm. D) d, 25 cm E) d, 60 cm 6. An object is placed 10 cm in front of a convex mirror that has a focal length of-15 cm. What is the magnification? Use a positive magnification for an crect image and negative for an inverted. A) 0.3 B) 0.6 C) 0.667 D) -1.67 E) -6 7. The near point of an eye is 125 cm, A corrective lens is to be used to allow this eye to focus clearly on objects 25 cm in front of it. What is the power of the needed corrective ens? A) +3.2 diopters B) +3.6 diopters C) +4.0 diopters D) +4.8 diopters E) +5.5 diopters

Explanation / Answer

4. f = 25 cm

do = 75 cm

Applying 1/f = 1/do + 1/di

1/25 = 1/75 + 1/di

di = 37.5 cm

Ans(B)

5. f = 15 cm

m = - 3 = - di / do

di = 3 do

1/f = 1/di + 1/do

1/15 = 1/3do + 1/do

1/15 = 1.33 / do

do = 20 cm

Ans(C)

6. 1/-15 = 1/10 + 1/di

di = - 6

m = - di / do = 0.6

Ans(B)

7. 1/f = 1/25 + 1/125

f= 20.8 cm = 0.208 m

D = 1/f = 4.8 D

Ans(D)

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