Optics & Waves · GCSE Physics Topic 6
Snell's Law & Fisherman Spearing Fish Refraction Simulator
Key exam takeaway: Refraction bends light away from normal when leaving water, making fish appear shallower. Spear below the virtual image, but point laser directly at it by reversibility of light.
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- Live Derivation
- Projector Mode
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3D Simulation Stage● 60 FPS
Parameter Controls
°
m
Live Derivations & Metrics
Refracted Angle θ2
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Critical Angle θc
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Apparent Depth
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TIR Phenomenon
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Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: Light enters glass (n=1.414) at 45° from air. Find angle of refraction and critical angle.
Step-by-Step Derivation:
- 1.0*sin(45°) = 1.414*sin(θ2) => sin(θ2) = 0.5 => θ2 = 30°. Critical angle sin(θc) = 1/1.414 => θc = 45°.
Worked Problem
Problem: A pool is 2m deep (n=1.333). Viewed from directly above, what is the apparent depth of the bottom?
Step-by-Step Derivation:
- Apparent depth h_app = h_real / n = 2 / 1.333 ≈ 1.5m. The pool appears 0.5m shallower than it is.
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: Viewed by a scuba diver looking up from water, do shore trees appear taller or shorter?
Answer Key: Taller! Light refracts toward normal entering water. Diver's back-projected sightline places tree tops higher.
Q2. Variant 2: What two conditions are necessary for total internal reflection? How does fiber optics utilize it?
Answer Key: 1) From denser to rarer medium (n1 > n2); 2) incident angle exceeds critical angle. Fiber core n > cladding n keeps light trapped inside.
Q3. Variant 3: Light traverses a flat glass slab. What happens to the exiting ray compared to the incident ray?
Answer Key: The exiting ray remains strictly parallel to the incident ray, experiencing only a lateral parallel displacement.
Frequently Asked Questions & Misconceptions
Why does a spear require aiming below the fish while a laser needs direct aim?
Spear travels in a straight line unaffected by refraction. Laser is light, and by reversibility of light, refracts along the identical path back to the real fish.
Why do hot asphalt roads appear to have water puddles in the distance in summer?
Inferior mirage. Blistering tarmac heats surface air, lowering refractive index. Downward skylight undergoes total internal refraction, creating illusory reflections.
Why do diamonds sparkle far more brilliantly than glass gemstones?
Diamonds have a high refractive index (n=2.42) and small critical angle (24.4°). Light undergoes multiple total internal reflections before exiting.
Why does a chopstick submerged in water appear bent upward at the surface?
Light from the submerged section bends away from normal upon exiting water. Apparent depth is shallower, making the stick look bent.