Visible light for OCR GCSE Physics
This page covers the following topics:
1. Visible light spectrum
2. Colours of objects
3. Types of reflection
4. Colour filters
5. Transparency and translucency
Visible light is a spectrum of colours found in the electromagnetic spectrum. In increasing frequency, it is made up of: red, orange, yellow, green, blue, indigo, violet. Each colour has its own small range of wavelength and frequency.
Light falling onto an object is either reflected or absorbed. The colour of an object that appears to be opaque can be found by determining the wavelength of the light it reflects, since this reflected light is what is detected by the human eye. If it reflects all wavelengths, then the object is white, whereas if it absorbs all wavelengths, then it is black.
Specular reflection occurs when light is reflected off of a smooth flat surface in only one direction. This is the type of reflection that occurs in a mirror, giving rise to an image in it which is upright and virtual. Diffuse reflection occurs when light is reflected off of a rough surface, scattering the light in many different directions. This could cause a distorted image of the object.
When light passes through a colour filter, some of it is absorbed and some is transmitted. The colour filter allows for the light rays which have the same colour with it to go through and absorbs the rest of all other colours. When white lights passes through a filter, all colours are absorbed except for the colour of the filter, which goes through.
Transparent objects are ones that trasmit light with very little absorption, allowing the light rays to go straight through. Translucent objects are ones that transmit some light but are not completely clear, due to some ongoing absorption. The light that is let to pass through a translucent object is randomly scattered.
Explain whether the given diagram shows a transparent or a translucent object.
Some light rays are absorbed by the object and the transmitted light is scattered, therefore the object must be translucent.
Explain whether the law of reflection holds for diffuse reflection.
The law of reflection states that the angle of incidence is equal to the angle of reflection. Individual light rays do still obey this law, however the different rays are reflected in different directions, since their angles of incidence are different from each other due to the fact that the surface is rough.
Michael is looking at a lamp emitting green light through a violet colour filter. Describe what he sees.
Since the light emitted by the lamp is a different colour to that of Michael's colour filter, none of the light will be transmitted into his eyes. Therefore, Michael will see no light coming from the lamp and he will only see black.
What is specular reflection?
Specular reflection is the type of reflection that occurs when light is reflected off of a smooth flat surface in one single direction.
The frequency of a light wave is measured to be 525 THz. State the colour of the wave.
525 THz falls into the range of the green colour region.
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