✓ 1 MARKS
MCQ
🔥 APPEARED IN 3 BOARD SETS
A thin plano-convex lens and a thin equi-concave lens are kept coaxially in contact as shown in the figure. Assuming both the lenses are made of glass of refractive index $\mu$, and R is the radius of curvature of each curved surface, the focal length of the combination is :
A
$\frac{\text{R}}{\mu - 1}$
B
$-\frac{\text{R}}{\mu - 1}$
C
$\frac{2\text{R}}{\mu - 1}$
D
$-\frac{2\text{R}}{\mu - 1}$
01 // VERIFIED BOARD OCCURRENCES
| Year | Paper Code | Set | Position |
|---|---|---|---|
| CBSE 2026 | Series 55-3 | Set 1 | Question 4 |
| CBSE 2026 | Series 55-3 | Set 2 | Question 12 |
| CBSE 2026 | Series 55-3 | Set 3 | Question 6 |
02 // OFFICIAL CBSE MARKING SCHEME BREAKDOWN
- Step 1: Stating the fundamental formula / law statement (+1 Mark)
- Step 2: Intermediate mathematical substitution or proof steps (+1 Mark)
- Step 3: Correct final value or conclusion with mandatory SI units (+1 Mark)