Refraction of light at plane surfaces — Flashcards
Telangana Board · Class 9 · Physical Science
20 flashcards for Refraction of light at plane surfaces (Telangana Board Class 9 Physical Science) to test yourself on key terms and facts.
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A pencil placed in a glass of water appears bent at the water surface. Explain why this happens.
Answer
This occurs due to refraction of light. Light rays from the pencil change direction when they pass from water (denser medium) to air (rarer medium). The light bends away from the normal, making the pe…
What is refraction of light?
Answer
Refraction is the bending of light when it passes from one transparent medium to another due to change in speed of light. The light ray changes direction at the interface between two media, except whe…
Calculate the refractive index of glass if light travels at 2×10⁸ m/s in glass. (Speed of light in vacuum = 3×10⁸ m/s)
Answer
Refractive index (n) = Speed of light in vacuum / Speed of light in medium n = c/v = (3×10⁸ m/s) / (2×10⁸ m/s) = 1.5 Therefore, the refractive index of glass is 1.5.
Why does light bend when it enters a different medium?
Answer
Light bends because its speed changes when entering a different medium. According to Fermat's principle, light takes the path that requires minimum time. When light speed changes at the interface, the…
What happens to light when it passes from air to water at 30° angle of incidence? (Refractive index of water = 1.33)
Answer
Using Snell's law: n₁sin i = n₂sin r 1 × sin 30° = 1.33 × sin r 0.5 = 1.33 × sin r sin r = 0.5/1.33 = 0.376 r = 22.1° The light ray bends toward the normal, with angle of refraction = 22.1°…
State Snell's Law and write its mathematical form.
Answer
Snell's Law states that for a ray of light passing from one medium to another, the ratio of sine of angle of incidence to sine of angle of refraction is constant. Mathematical form: n₁ sin i = n₂ sin …
A coin at the bottom of a water-filled vessel becomes visible when water is added. How does this happen?
Answer
Initially, light from the coin cannot reach the eye due to the vessel's walls. When water is added, light from the coin refracts at the water-air interface, bending away from the normal. This refracte…
What is critical angle and how is it calculated?
Answer
Critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°. The refracted ray grazes the interface. Formula: sin C = n₂/n₁ = 1/n₂₁ Where…
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