At what angle must a light ray fall on the surface of an equilateral prism so that its angle of minimum deviation will be 20°?
OR
Calculate the time required by a ray of light to traverse a glass slab of thickness 2 mm. The refractive index of glass=1.5.
WBBSE
Class X
Physical Science
Light – Reflection and Refraction
02 Mark
2024
Angle of the prism = 60°
Angle of minimum deviation (δ) = 20°
We know,
Angle of minimum deviation (δ) = 2i – A
or, δ = 2i – A
or, 2i = δ + A = 20° + 60° = 80°
or, i = 40°
OR
Given
- Distance = 2 mm = 2 × 10⁻³ m
- Speed of light in vacuum (c) = 3 × 10⁸ m/s
- Refractive index of glass (μ) = 1.5
μ = \text{c}\over\text{v}
or, v = \text{c}\over\text{μ}
= \text{3 × 10⁸}\over\text{1.5}
= 2 × 10⁸ m/s
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