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A real image of an object is formed at a distance of 20 cm from a lens. On putting another lens in contact with it, the image is shifted 10 cm towards the combination. The power of the lens is
- a)2 D
- b)5 D
- c)6 D
- d)10 D
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
A real image of an object is formed at a distance of 20 cm from a lens...
As image formed is real, therefore lens must be convex, v = 20cm.
Let f1, be the focal length for this lens and f2 be the focal length of the other lens put in contact later.
for the first lens,
After placing it in contact with another lens, the image shifted to 10cm towards the combination
i.e., v2 = (20 − 10) cm = 10 cm
Let fnet be the effective focal length of the combination, which can be given as:
From equation (1) and (2):
Hence, f2 = 20cm
Let f1, be the focal length for this lens and f2 be the focal length of the other lens put in contact later.
for the first lens,
After placing it in contact with another lens, the image shifted to 10cm towards the combination
i.e., v2 = (20 − 10) cm = 10 cm
Let fnet be the effective focal length of the combination, which can be given as:
From equation (1) and (2):
Hence, f2 = 20cm
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Community Answer
A real image of an object is formed at a distance of 20 cm from a lens...
Given Data:
- Distance of real image from lens = 20 cm
- Shift of image after adding another lens = 10 cm
Calculating the Power of the Lens:
- The formula for power of a lens is:
Power = 1/f
- Using the lens formula:
1/f = 1/v - 1/u
where f is the focal length, v is the image distance, and u is the object distance
Calculation:
- Initially, the image distance v = 20 cm
- The object distance u = -20 cm (since the image is formed on the same side as the object)
- Therefore, the focal length f = 1/(1/v - 1/u) = 1/(1/20 + 1/20) = 10 cm
- After adding another lens, the image shifts 10 cm towards the combination. This means the new image distance v' = 10 cm
- The object distance u' = -30 cm (20 cm initial distance - 10 cm shift)
- The new focal length f' = 1/(1/v' - 1/u') = 1/(1/10 + 1/30) = 5 cm
Calculating the Power of the Combination:
- The total power of the combination of lenses is the sum of the individual powers:
Power(combination) = Power(lens1) + Power(lens2) = 1/f + 1/f'
- Substituting the values:
Power(combination) = 1/10 + 1/5 = 0.1 + 0.2 = 0.3 D
Therefore, the power of the lens is 5 D (option B).
- Distance of real image from lens = 20 cm
- Shift of image after adding another lens = 10 cm
Calculating the Power of the Lens:
- The formula for power of a lens is:
Power = 1/f
- Using the lens formula:
1/f = 1/v - 1/u
where f is the focal length, v is the image distance, and u is the object distance
Calculation:
- Initially, the image distance v = 20 cm
- The object distance u = -20 cm (since the image is formed on the same side as the object)
- Therefore, the focal length f = 1/(1/v - 1/u) = 1/(1/20 + 1/20) = 10 cm
- After adding another lens, the image shifts 10 cm towards the combination. This means the new image distance v' = 10 cm
- The object distance u' = -30 cm (20 cm initial distance - 10 cm shift)
- The new focal length f' = 1/(1/v' - 1/u') = 1/(1/10 + 1/30) = 5 cm
Calculating the Power of the Combination:
- The total power of the combination of lenses is the sum of the individual powers:
Power(combination) = Power(lens1) + Power(lens2) = 1/f + 1/f'
- Substituting the values:
Power(combination) = 1/10 + 1/5 = 0.1 + 0.2 = 0.3 D
Therefore, the power of the lens is 5 D (option B).
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A real image of an object is formed at a distance of 20 cm from a lens. On putting another lens in contact with it, the image is shifted 10 cm towards the combination. The power of the lens isa)2 Db)5 Dc)6 Dd)10 DCorrect answer is option 'B'. Can you explain this answer? for NEET 2025 is part of NEET preparation. The Question and answers have been prepared according to the NEET exam syllabus. Information about A real image of an object is formed at a distance of 20 cm from a lens. On putting another lens in contact with it, the image is shifted 10 cm towards the combination. The power of the lens isa)2 Db)5 Dc)6 Dd)10 DCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for NEET 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A real image of an object is formed at a distance of 20 cm from a lens. On putting another lens in contact with it, the image is shifted 10 cm towards the combination. The power of the lens isa)2 Db)5 Dc)6 Dd)10 DCorrect answer is option 'B'. Can you explain this answer?.
A real image of an object is formed at a distance of 20 cm from a lens. On putting another lens in contact with it, the image is shifted 10 cm towards the combination. The power of the lens isa)2 Db)5 Dc)6 Dd)10 DCorrect answer is option 'B'. Can you explain this answer? for NEET 2025 is part of NEET preparation. The Question and answers have been prepared according to the NEET exam syllabus. Information about A real image of an object is formed at a distance of 20 cm from a lens. On putting another lens in contact with it, the image is shifted 10 cm towards the combination. The power of the lens isa)2 Db)5 Dc)6 Dd)10 DCorrect answer is option 'B'. Can you explain this answer? covers all topics & solutions for NEET 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A real image of an object is formed at a distance of 20 cm from a lens. On putting another lens in contact with it, the image is shifted 10 cm towards the combination. The power of the lens isa)2 Db)5 Dc)6 Dd)10 DCorrect answer is option 'B'. Can you explain this answer?.
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