NEET UG · Physics · Ray Optics and Optical Instruments

Thin Lens Formula: NEET previous year questions

9 questions in ten years of NEET, in 6 of 10 papers. Pattern: Every year. Here is how it is asked and which ideas come back.

Asked in 10 years: 9; about 0.8 per paper
Years asked: 6/10; last asked 2026
Chance of a question next paper: 64%; historical rate, how we compute it
Weighted estimate: 1.1; model; history: 0.9 a paper on average, typically 0–2

Key findings

01
Asked in 6 of 10 papers, 9 questions in all: #86 of 204 topics by ten-year total. It comes back every 1.4 years on average.
02
78% of its questions since 2018 tested an idea never asked before; none repeated an idea from the year before.
03
The most repeated idea is Combination of Lenses Separated by a Distance, asked 2 times (2021, 2026), usually as “numerical”.
04
NEET has asked 6 of the 75 ideas in this topic; 65 have never been asked, directly or indirectly.
05
Mostly asked as one-line MCQ (44%); 33% easy, 22% hard.

Questions per year

Up to 2023: 0.8; per paper
Since 2024: 1.0; 0.2
Usual gap: 1.4 yrs; between papers asking it
Swing: ±0.8; questions, year to year

Revise first

Combination of Lenses Separated by a Distance (2021 2026); Combination of Thin Lenses (2023 2025); Index Correction on the Optical Bench (2026)

How it is asked

Difficulty, format and skill

Across all 9 questions on Thin Lens Formula since 2017.

Difficulty

QUESTIONS

342

Easy3 · 33%
Medium4 · 44%
Hard2 · 22%

Format

One-line MCQ · 4 Q44%
Numerical · 3 Q33%
Figure-based · 2 Q22%

Skill tested

Multi-step · 4 Q44%
Concept · 2 Q22%
Calculation · 2 Q22%
Recall · 1 Q11%

Repeats

New idea, or one asked before?

Each column is a paper. Blue questions tested an idea NEET had not asked before; navy ones went back to an idea from an earlier paper. 2017 is the first paper, so everything in it counts as new.

’17’18’19’20’21’22’23’24’25’26

Idea asked for the first time
Idea asked in an earlier paper

Coverage of the topic

NEET has asked 6 of the 75 ideas in this topic. 65 have never been asked yet.

Asked directly6 · 8%
Touched inside another question4 · 5%
Never asked65 · 87%

Ideas come from Lumi’s syllabus map of NCERT. A never-asked idea is not a safe skip: most new questions come from exactly these.

Drill down

Idea, year, question

Every idea NEET tested in this topic, with its ten papers. Open one to read the questions.

ideaAskedShareYears’17’18’19’20’21’22’23’24’25’26

Repeated2 · 22%22%2/10
- 2026 · Q29
  The lens combination as shown in the figure, consists of two lenses, $L_1$ and $L_2$ , of the focal lengths +10 cm and $-10$ cm,…
  mediumFigure-based
- 2021 · Q17
  A convex lens 'A' of focal length 20 cm and a concave lens 'B' of focal length 5 cm are kept along the same axis with a distance 'd'…
  mediumNumericalNew idea
Repeated2 · 22%22%2/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10

Squares are the ten papers, 2017 to 2026; darker means more questions. Share is of the level above.

Ideas

Every idea inside this topic

7 different ideas were tested; 2 came more than once. Thin Lens Formula Application is the foundation for 42 other ideas in the syllabus.

Combination of Lenses Separated by a Distance2×
numerical
Figure-based · 6% next · foundation for 3
Combination of Thin Lenses2×
equivalent focal length of lenses in contact
One-line MCQ · 6% next · foundation for 8
Index Correction on the Optical Bench1×
identify measurement needing index correction
One-line MCQ · 6% next
Lens Maker's Formula1×
numerical
Figure-based · 4% next · foundation for 23
Optical Power Calculation1×
numerical
Numerical · 4% next · foundation for 15
Thin Lens Formula Application1×
final image position for lens and plane mirror
One-line MCQ · 4% next · foundation for 42
Liquid Trapped Between Two Lenses1×
numerical
Numerical · 4% next

Idea	Times	Format	Chance next	Foundation for
Combination of Lenses Separated by a Distancenumerical	2	Figure-basedCalculation	6%	3 ideas
Combination of Thin Lensesequivalent focal length of lenses in contact	2	One-line MCQConcept	6%	8 ideas
Index Correction on the Optical Benchidentify measurement needing index correction	1	One-line MCQRecall	6%	–
Lens Maker's Formulanumerical	1	Figure-basedMulti-step	4%	23 ideas
Optical Power Calculationnumerical	1	NumericalCalculation	4%	15 ideas
Thin Lens Formula Applicationfinal image position for lens and plane mirror	1	One-line MCQMulti-step	4%	42 ideas
Liquid Trapped Between Two Lensesnumerical	1	NumericalMulti-step	4%	–

Chance next is the historical rate at which an idea with this record came back in the following paper. It is low for every idea, which is why learning the topic beats memorising past questions. All repeated ideas

Every question

Thin Lens Formula questions, year by year

The opening words of each question as it appeared in the official paper, with the idea it tested.

NEET 20262 questions

Q20
Which of the following measurements require 'index correction' ?
Idea: Index Correction on the Optical Bench
New ideaMediumOne-line MCQ
Q29
The lens combination as shown in the figure, consists of two lenses, $L_1$ and $L_2$ , of the focal lengths +10 cm and $-10$ cm,…
Idea: Combination of Lenses Separated by a Distance
MediumFigure-based · figure

NEET 20251 question

Q13
In a certain camera, a combination of four similar thin convex lenses are arranged axially in contact. Then the power of the combination…
Idea: Combination of Thin Lenses
EasyOne-line MCQ

NEET 20232 questions

Q45
In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin)?
Idea: Lens Maker's Formula
New ideaHardFigure-based · figure
Q46
Two thin lenses are of same focal lengths ( $f$ ), but one is convex and the other one is concave. When they are placed in contact with each…
Idea: Combination of Thin Lenses
New ideaEasyOne-line MCQ

NEET 20221 question

Q29
A biconvex lens has radii of curvature, 20 cm each. If the refractive index of the material of the lens is 1.5, the power of the lens is :
Idea: Optical Power Calculation
New ideaEasyNumerical

NEET 20212 questions

Q17
A convex lens 'A' of focal length 20 cm and a concave lens 'B' of focal length 5 cm are kept along the same axis with a distance 'd'…
Idea: Combination of Lenses Separated by a Distance
New ideaMediumNumerical
Q50
A point object is placed at a distance of 60 cm from a convex lens of focal length 30 cm. If a plane mirror were put perpendicular to the…
Idea: Thin Lens Formula Application
New ideaHardOne-line MCQ · figure

NEET 20191 question

Q11
Two similar thin equi-convex lenses, of focal length f each, are kept coaxially in contact with each other such that the focal length of…
Idea: Liquid Trapped Between Two Lenses
New ideaMediumNumerical

Questions from the official NEET UG papers published by NTA (CBSE before 2019). Topic and idea tags, counts and notes are Lumi’s.