JEE Main 2025 Jan 28 Shift 1, Physics Q20: Prism

JEE Main2025Jan 28, Shift 1Physics

A thin prism $P_{1}$ with angle 4° made of glass having refractive index 1.54, is combined with another thin prism $P_{2}$ made of glass having refractive index 1.72 to get dispersion without deviation. The angle of the prism $P_{2}$ in degrees is

A
$4$
B
$3$
C
$16/3$
D
$1.5$

Solution

For a thin prism, the deviation is $δ = (μ - 1) A$ . "Dispersion without deviation" means the two prisms are placed with opposite orientations so that net mean deviation vanishes:

$(μ_{1} - 1) A_{1} = (μ_{2} - 1) A_{2}$

Plug in: $(1.54 - 1) (4°) = (1.72 - 1) A_{2}$

$0.54 \times 4 = 0.72 \times A_{2} \Rightarrow A_{2} = \frac{2.16}{0.72} = 3°$ .

$∴ A_{2} = 3°$ .

Concept behind this question

PrismNotes, formulas and examples →

Practice more Physics

Concept-wise practice with instant solutions on Fundamenthol.

Start practicing →

JEE Main 2025 Jan 28 Shift 1, Physics Q20: Prism

Concept behind this question

More previous year questions on Prism

Practice more Physics