How to get the solution: 1) If a camera has a 177 mm focal length lens, how far

Question

How to get the solution:

1) If a camera has a 177 mm focal length lens, how far is the lens from the film (in mm) when focusing on an object 4.4 m away?          The answer is: 184

2) If a farsighted eye has a near point of 66 cm and it is to be adjusted to 25 cm by use of an lens, what focal length (in cm) is required? (Assume the lens is very close to the eye.   The answer is: 40.2

3) If the focal length of a lens is 15.2 cm, what is its lens power?     The answer is: 6.6

4) An object is placed 11.9 cm in front of a converging lens with a focal length of 39.5 cm, its image is at

           The answer is: -17

5) If the radius of curvature of the first surface is +35 cm and the second surface has a radius of -43 cm , for the lens (n=1.5), it has a focal length of

      The answer is: 376.2

Explanation / Answer

part 1 )

1/v + 1/u = 1/f

v = image distance

u = object distance

1/4400 +1/v = 1/177

1/v = 1/177 - 1/4400

v = 184.4 = 184 mm

part 2 )

1/u + 1/v = 1/f

u = 25 cm

v = -66 cm

1/f = 1/25 - 1/66

f = 40.2 cm

part 3 )

P = 1/f

f = 15.2 cm = 15.2 x 10^-2 m

P = 6.57 = 6.6

part 4 )

1/u + 1/v = 1/f

1/v = 1/39.5 - 1/11.9

v = -17.03 = -17 cm

part 5 )

1/f = [(n_lens - no)/no ] * (1/R1 - 1/R2)

f = 38.58974 cm

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