Topic 5.1-5.3 — Light and Colour Flashcards
(10 cards)
Explain reflection
The angle of incidence = the angle of reflection
Angles are always measured from the normal.
Waves reflect at the boundary between 2 different materials.
Explain refraction
Refraction is the change in direction of a wave at a boundary between 2 transparent materials.
If entering a denser material, it bends towards the normal. If entering a less dense material, it bends away from the normal.
Explain total internal reflection
When a light ray is passing from a denser medium to a less dense medium and the ray is brought out at more than 90° from the normal the refraction is not possible. Therefore, the ray is reflected inside the more dense medium following the law of reflection. The angle of incidence when the ray changes from just refraction to total internal reflection is called the critical angle.
If the angle of incidence is equal to the critical angle, the reflected ray will pass along the boundary and not exit the medium
For glass to air how does light react?
-If the angle is less than the critical angle, light refracts away from the normal
-If the angle is equal to the critical angle, light passes along the boundary
-If the angle is more than the critical angle, light reflects
Describe specular reflection
In specular reflection, waves are reflected from a smooth, flat surface and all exit at the same angle. The image is upright and virtual.
Describe diffuse reflection
When light hits a rough surface, diffuse reflection occurs. Instead of forming an image the reflected light is scattered in all directions. This may cause a scattered or no image.
Describe colours in terms of light
Each colour within the visible light spectrum (ROYGBIV) has its own narrow band of wavelength and frequency. ROYGBIV goes in order of increasing frequency and decreasing wavelength.
An object appears to be black if it absorbs all the wavelengths of visible light (e.g. a blue object in red light).
White light reflects all colours
Explain how colour of light is related to differential absorption at surfaces
Waves can be absorbed at the boundary between 2 different materials. When waves are absorbed by a surface, the energy of the wave is transferred to the particles in the surface. This will usually increase the internal energy of the particles.
When white light shines on an opaque object, some wavelengths or colours of light are absorbed. These wavelengths are not detected by our eyes. The other wavelengths are reflected, and these are detected by our eyes.
Explain transmission of light waves
Waves can be transmitted at the boundary between 2 different materials. When waves are transmitted the wave continues through the material. Transparent materials are very good at transmitting light with very little absorption. Translucent materials transmit some light
Explain how colour of light is related to the transmission of light through filters
When white light passes through a coloured filter, all colours are absorbed except for the colour of the filter.
