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P6 D) Waves at Boundaries – Reflection
P6 D) Waves at Boundaries – Reflection
Three things can happen when a wave hits a boundary between two materials; the wave can be absorbed, transmitted or reflected.
1) Absorbed
Waves can be absorbed by the second material. When waves are absorbed, energy is transferred from the wave to an energy store in the second material (the energy store is usually thermal). An example of waves being absorbed is leaving your phone outside on a sunny day. When you leave your phone outside on a sunny day, infrared waves from the sun are absorbed by the phone’s screen, which results in the phone’s screen becoming hot. Another example of waves being absorbed is sound waves being absorbed by a thick curtain in a room.
2) Transmitted
Waves can be transmitted, which is where the waves travel through the second material. An example of waves being transmitted is light travelling through air and entering a glass block. When light enters glass at an angle, the speed and direction of light changes; this is known as refraction.
3) Reflected
Waves can also be reflected by the second material. Reflection is where a wave is sent back away from the second material. Mirrors reflect light waves, and walls reflect sound waves (echoes).
Note
What happens to waves at the boundaries between different substances depends on the properties of the materials involved and the wavelengths of the waves.
1) Absorbed
Waves can be absorbed by the second material. When waves are absorbed, energy is transferred from the wave to an energy store in the second material (the energy store is usually thermal). An example of waves being absorbed is leaving your phone outside on a sunny day. When you leave your phone outside on a sunny day, infrared waves from the sun are absorbed by the phone’s screen, which results in the phone’s screen becoming hot. Another example of waves being absorbed is sound waves being absorbed by a thick curtain in a room.
2) Transmitted
Waves can be transmitted, which is where the waves travel through the second material. An example of waves being transmitted is light travelling through air and entering a glass block. When light enters glass at an angle, the speed and direction of light changes; this is known as refraction.
3) Reflected
Waves can also be reflected by the second material. Reflection is where a wave is sent back away from the second material. Mirrors reflect light waves, and walls reflect sound waves (echoes).
Note
What happens to waves at the boundaries between different substances depends on the properties of the materials involved and the wavelengths of the waves.
Reflection
Reflection is where a wave is sent back away from a second material. Mirrors reflect light waves, and walls reflect sound waves (echoes). The law of reflection states that:
Reflection is where a wave is sent back away from a second material. Mirrors reflect light waves, and walls reflect sound waves (echoes). The law of reflection states that:
These angles are worked out relative to the normal. The incidence ray is the ray that is hitting the surface (mirror), and the reflected ray is the ray that is coming back off of the surface (mirror). The diagram below shows the surface (mirror), incident ray, reflected ray, normal, angle of incidence and angle of reflection.
The normal is an imaginary line that is perpendicular (at 90°) to the surface that is doing the reflecting. The normal is also the line where the incident ray (the ray hitting the surface) and the reflected ray (the ray coming away from the surface) travel along the same path/ line. We look along the normal when we look at ourselves in a mirror.
From the above diagram, we can see that the angle of incidence is the same as the angle of reflection.
Smooth surfaces produce strong reflections; a mirror is a smooth surface, which produces a perfect image when you look at it. Rough surfaces diffuse reflections, which produces images or echoes that are less clear.
From the above diagram, we can see that the angle of incidence is the same as the angle of reflection.
Smooth surfaces produce strong reflections; a mirror is a smooth surface, which produces a perfect image when you look at it. Rough surfaces diffuse reflections, which produces images or echoes that are less clear.