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Two thin lenses of power +3.5 D and -2.5 D are placed in contact. Find the focal length of the lens combination.​
  • a)
    16.7 m
  • b)
    1 cm
  • c)
    -16.7 m
  • d)
    100 cm
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
Two thin lenses of power +3.5 D and -2.5 D are placed in contact. Find...
Explanation:
When two thin lenses of power P1 and P2 are placed in contact, the power of the combination (P) is given by:
1/P = 1/P1 + 1/P2
Here, P1 = 3.5 D and P2 = -2.5 D
Substituting the values in the above formula, we get:
1/P = 1/3.5 - 1/2.5
1/P = 0.2857 - 0.4
1/P = -0.1143
P = -8.75 D
The focal length (f) of a lens is given by:
f = 1/P
Substituting the value of P, we get:
f = 1/-8.75
f = -0.1143 m or -11.43 cm or -114.3 mm
Since the focal length cannot be negative, we take the absolute value of f, which is:
f = 11.43 cm or 114.3 mm
Therefore, the correct answer is option D, 100 cm.
Free Test
Community Answer
Two thin lenses of power +3.5 D and -2.5 D are placed in contact. Find...
The power of combined lenses is the sum of the power of individual lens and focal length = 1/power of the lens.
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Two thin lenses of power +3.5 D and -2.5 D are placed in contact. Find the focal length of the lens combination.​a)16.7 mb)1 cmc)-16.7 md)100 cmCorrect answer is option 'D'. Can you explain this answer?
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