Reflection (Edexcel GCSE Physics): Revision Notes
📚 Revision Notes
Reflexion
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Waves can be reflected, absorbed, or transmitted at the boundary between two different materials.
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Reflection occurs when a wave hits a surface and bounces back into the original medium instead of passing through the surface. This is similar to how a ball bounces off a wall.
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Method
- Draw on the 'normal'. The 'normal' is simply another word for a line that is at 90 degrees to the boundary.
- Draw the incident ray. Using a protractor, measure out an angle. Using a ruler, draw a straight line along the angle to create the incident ray.
- Draw on the reflected ray. Again, take your protractor and measure out the same angle as before. This time, you should be measuring the angle on the opposite side. Draw a straight line along this angle, ensuring that it touches the normal.
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You should be able to draw out ray diagrams to show the reflections of waves at a surface. To do this, you will need a sharp pencil, a ruler and a protractor.
Ray Diagrams
- The 2 types of reflected waves are different. When there is specular reflexion, the reflected wave will have the same angle of reflexion as the angle of incidence. When there is diffuse reflexion, the reflected wave will have a different angle of reflexion compared to the angle of incidence.
- There are 2 types of reflexion. When we talk about reflexion, there can be two types. They are called specular reflexion and diffuse reflexion. Specular reflection occurs when waves hit a smooth surface, whilst diffuse reflection occurs when the waves hit a distorted, uneven surface.
Reflexion
- Waves will reflect off a flat surface
- The smoother the surface, the stronger the reflected wave is
- Rough surfaces scatter the light in all directions, so they appear matt and not reflective
- The angle of incidence = angle of reflexion
- Light will reflect if the object is opaque and is not absorbed by the material
- The electrons will absorb the light energy, then reemit it as a reflected wave
Transmission
- Waves will pass through a transparent material
- The more transparent, the more light will pass through the material
- It can still refract, but the process of passing through the material and still emerging is transmission
Absorption
- If the frequency of light matches the energy levels of the electrons
- The light will be absorbed by the electrons and not reemitted
- They will be absorbed and then reemitted over time as heat
- So that particular frequency has been absorbed
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If a material appears green, only green light has been reflected, and the rest of the frequencies in visible light have been absorbed