Change set
Pick exam & year, then Go.
Question map
Not attempted
Correct
Incorrect
★
Bookmarked
Loading…
Q121
(NDA-II/2024)
Science & Technology › Basic Science (Physics, Chemistry, Biology)
Official Key
Which one among the following is the correct focal length of a combination of lenses of power 2.5 D and -2·0 D ?
Result
Your answer:
—
·
Correct:
C
Explanation
The power of a combination of lenses is calculated as the algebraic sum of the individual powers of the lenses. According to the lens formula for combinations:
- Total Power (P) = P1 + P2
- Given: P1 = +2.5 D and P2 = -2.0 D
- P = 2.5 D + (-2.0 D) = +0.5 D
The relationship between the power of a lens and its focal length (f) is expressed by the formula P = 1/f, where the focal length is measured in meters. To find the focal length:
- f = 1 / P
- f = 1 / 0.5
- f = +2.0 m
Since the resultant power is positive, the combination behaves like a converging lens with a focal length of +2.0 m. Thus, Option C is the correct answer.
How others answered
Each bar shows the % of students who chose that option.
Green bar = correct answer, blue outline = your choice.
Community Performance
Out of everyone who attempted this question.
37%
got it right
✓ Thank you! We'll review this.
SIMILAR QUESTIONS
5 Cross-Linked PYQs
UPSC repeats concepts across years. Login to see how this question connects to 5 others.
Login with Google