Waves - 6.1.3 Reflections of Waves (Physics Only) (GCSE Physics AQA)

Reflections of Waves (Physics Only)

Waves at Boundaries

• Boundaries are found between materials. When two different materials are next to each other, there is a boundary between them. This boundary is the point at which one material ends and the other material starts.
• Waves can be reflected at boundaries. When waves are passing from one material to another, they will reach a boundary. At this boundary, the wave might actually be reflected and unable to pass into the second material.

• Waves can also be transmitted or absorbed. Instead of being reflected, the waves could also be absorbed or transmitted. If a wave is transmitted, this means that it simply passes from the first material into the second material. If a wave is absorbed, then the energy of the wave will be transferred to the energy store of the second material.

Reflections, Transmission and Absorption

• Transmission can lead to refraction. As a wave is transmitted from one material to the other, it can be refracted. Refraction is when a wave changes direction as it crosses a boundary. This means that the wave will enter the material in one direction and leave the material in another direction.

• Waves are reflected by the same angle. When a wave reaches a boundary, it will be reflected by the same angle at which it arrived. We can put this more simply by calling the arrival angle as the angle of incidence, and the reflected angle as the angle of reflection. They are linked by the following relationship.

• There are 2 types of reflection. When we talk about reflection, there can be two types. They are called specular reflection and diffuse reflection. Specular reflection occurs when waves hit a smooth surface, whilst diffuse reflection occurs when the waves hit a distorted, uneven surface.
• The 2 types of reflected waves are different. When there is specular reflection, the reflected wave will have the same angle of reflection as angle of incidence. When there is diffuse reflection, the reflected wave will have a different angle of reflection compared to the angle of incidence.

Ray Diagrams

For AQA exams, 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.

Method

1. Draw on the ‘normal’. The ‘normal’ is simply another word for a line that is at 90 degrees to the boundary.
2. 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.
3. 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.

Investigating Reflection of Light

Method

1. Gather the equipment. For this experiment, you will need a ray box, a piece of paper, a pencil, a surface and a protractor.
2. Set up the equipment. Place your surface onto the paper so that it lines up with one of the edges. Draw on the normal to the surface using your pencil. Place the ray box so that it can be aimed at the surface at different angles.

Investigating Refraction of Light

Method

1. Gather the equipment. For this experiment, you will need a ray box, a piece of paper, a pencil, a transparent block of material and a protractor.
2. Set up the equipment. Place the block in the centre of the piece of paper. Trace around the block. Position the ray box so that it can be aimed at the block.
3. Draw on the normal. Using a ruler and a protractor, draw on a line that is 90 degrees to the block. This will act as the normal.
4. Draw the incident ray. Using the protractor, measure an angle from the normal. Draw a line along this angle and then aim the light ray along it. Trace this ray; it is the incident ray. Make sure to label this ray with the angle.
5. Draw the emergent ray. When the ray box is aimed at the block, you will see the incident ray going into the block, and another ray coming out of the other side of the block. This is the emergent ray, which you should draw over using your pencil. Make sure to label this ray with the angle of the incident ray.