Light (Optics)
Nature of light, reflection, refraction, lenses and fibre optics.
Optics, summary notes
- Light travels in straight lines at ~3 × 10⁸ m/s in a vacuum, slower in denser media.
- Reflection: angle of incidence = angle of reflection (measured from the normal).
- Refraction: light bends when it crosses into a medium of different density (Snell's Law), why a straight rod looks bent when dipped in water.
- Lenses and mirrors form images according to the lens/mirror equation, used in borescopes, cockpit optics and landing light reflectors.
- Fibre optics rely on total internal reflection: light hitting the boundary of a denser-to-rarer medium beyond the critical angle reflects entirely rather than escaping, how aircraft data buses and borescopes work.
- Snell's Law
- n₁ sinθ₁ = n₂ sinθ₂
- Refractive index
- n = c / v
- Mirror / lens equation
- 1/f = 1/u + 1/v
- Critical angle
- sinθc = n₂ / n₁
Light travels from air (n = 1.0) into glass (n = 1.5) at an angle of incidence of 30°. Find the angle of refraction.
sinθ₂ = (n₁ sinθ₁)/n₂ = (1.0 × sin30°)/1.5 = 0.333. θ₂ = sin⁻¹(0.333) = 19.5°.
A fibre-optic core has n = 1.50 and its cladding has n = 1.44. Find the critical angle for total internal reflection.
sinθc = n₂/n₁ = 1.44/1.50 = 0.96. θc = sin⁻¹(0.96) = 73.7°, any light hitting the core-cladding boundary beyond this angle reflects entirely back into the core.
Optics concept map
Optics (Light)
Optics quiz
Light (Optics)
1. Light travels in:
Straight linesCurves alwaysCircles2. Light is a form of:
Electromagnetic energySoundMatter3. The speed of light in a vacuum is about:
3 × 10⁸ m/s3 × 10³ m/s340 m/s4. The bouncing of light off a surface is:
ReflectionRefractionDiffraction5. The law of reflection: the angle of incidence equals the angle of:
ReflectionRefractionIncidence doubled6. The bending of light as it enters a new medium is:
RefractionReflectionDispersion only7. Light bends on refraction because it changes:
Speed (medium)ColourFrequency only8. A mirror mainly causes:
ReflectionRefractionDiffraction9. A lens works mainly by:
RefractionReflectionConduction10. A convex (converging) lens brings parallel rays to a:
FocusParallel beamStandstill11. A concave (diverging) lens makes parallel rays:
Spread apartConverge to a pointStop12. The point where a converging lens focuses parallel light is the:
Focal pointCentre of curvatureObject13. The splitting of white light into colours is:
DispersionReflectionConduction14. A prism can produce a:
SpectrumMirror image onlyEcho15. The refractive index compares light's speed in a vacuum to its speed in the:
MediumSourceEye