Light Flashcards
What range of wavelengths does visible light occupy in the electromagnetic spectrum?
Roughly 400 nm (violet) to 700 nm (red).
Define wavelength and frequency.
Wavelength (λ) is the distance between identical points on consecutive waves; frequency (f) is the number of waves passing a point per second.
State the wave equation that links velocity, frequency and wavelength.
v = f × λ
What is specular reflection?
Reflection from a smooth surface where parallel incident rays remain parallel, producing a clear image.
What is diffuse reflection and why does it occur?
Reflection from a rough surface causing rays to scatter in many directions; surface irregularities change incident angles.
Explain how colour filters work.
They absorb certain wavelengths (colours) and transmit the rest, so only transmitted colours reach the eye.
Why does an opaque object appear a particular colour?
It reflects that colour’s wavelengths more strongly and absorbs others.
What colour does an object appear if it reflects all wavelengths equally?
White.
What colour does an object appear if it absorbs all visible wavelengths?
Black.
Distinguish between transparent and translucent materials.
Transparent: transmit light with little scattering, forming clear images. Translucent: transmit light but scatter it, producing blurred images.
State Snell’s Law for refraction.
n_1 sin θ_1 = n_2 sin θ_2 where n is refractive index and θ is angle to the normal.
What happens to light when it passes from a less dense to a more optically dense medium?
It bends towards the normal; speed decreases, wavelength shortens, frequency unchanged.
Define real and virtual images.
Real image: light rays converge to form it; can be projected on a screen. Virtual image: rays only appear to diverge from it; cannot be projected.
Describe image formation by a convex (converging) lens when the object is beyond 2F (twice focal length).
Image is real, inverted, smaller, formed between F and 2F on the opposite side.
Describe the image formed by a concave (diverging) lens for any object position.
Always virtual, upright, diminished, located on the same side as the object.
State the lens equation.
1/f = 1/u + 1/v where f is focal length, u object distance, v image distance (convention: real distances positive).
How is magnification calculated for lenses?
Magnification = image height / object height = v / u (unit‑less).
Draw‑symbol convention in ray diagrams: how are convex and concave lenses represented?
Convex: straight vertical line with outward arrows top & bottom. Concave: straight vertical line with inward arrows.
Required Practical 6 — key sources of error when measuring angles of incidence and refraction in glass blocks?
Thickness of ray lines, protractor mis‑reading, block movement; minimise by using sharp pencils, repeated readings, normal drawn precisely.
What is infra‑red radiation and how does emission vary with temperature?
Electromagnetic radiation of wavelengths longer than visible light; hotter bodies emit more IR per unit time and at shorter peak wavelengths.
Define a perfect black body.
An object that absorbs all incident radiation and is also the best possible emitter.
Explain black‑body radiation curves.
Intensity vs wavelength graphs where increasing temperature shifts the peak to shorter wavelengths and raises overall intensity.
Why does Earth’s surface temperature depend on the balance between absorbed and emitted radiation?
If absorption > emission, temperature rises; if emission > absorption, temperature falls, until equilibrium is restored.
Give two everyday examples illustrating colour filters and differential absorption.
Red glass transmits red light, absorbing others; green leaves appear green because chlorophyll reflects green but absorbs red/blue.
