The law of reflection, why refraction happens at a boundary, how we hear, ultrasound, and what seismic waves reveal about the structure of the Earth. Physics only content.
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1.State the law of reflection.
The angle of incidence equals the angle of reflection.
2.What is the normal?
A construction line drawn at right angles to the surface at the point where the ray hits it.
3.Are angles measured from the surface or the normal?
Always from the normal.
4.What is specular reflection?
Reflection from a smooth surface in a single direction, producing a clear image.
5.What is diffuse reflection?
Reflection from a rough surface, scattering the light in all directions.
6.Why can you not see your reflection in a wall?
The surface is rough, so light is reflected diffusely in all directions rather than forming an image.
7.What is refraction?
The change in direction of a wave as it crosses a boundary between two materials.
8.What causes refraction?
The wave changes speed when it enters a different material.
9.Which way does light bend entering a denser material?
Towards the normal, because it slows down.
10.Which way does light bend leaving a denser material?
Away from the normal, because it speeds up.
11.When does a wave not change direction at a boundary?
When it hits the boundary along the normal, at 90 degrees to the surface.
12.What happens to wavelength during refraction?
It changes with the speed. The frequency stays the same.
13.What can happen to a wave at a boundary, other than refraction?
It can be reflected, absorbed, or transmitted.
14.What kind of wave is sound?
A longitudinal wave.
15.How does sound travel through a solid?
The vibrations are passed on from particle to particle through the material.
16.What is the range of human hearing?
About 20 Hz to 20 000 Hz.
17.How do we hear sound?
Sound waves make the ear drum vibrate, the vibrations are passed through small bones to the cochlea, which converts them into electrical signals sent to the brain.
18.Why is human hearing limited in range?
The conversion of sound waves to vibrations in the ear only works efficiently over a limited range of frequencies.
19.What is ultrasound?
Sound with a frequency above 20 000 Hz, higher than the human hearing range.
20.What happens to ultrasound at a boundary between media?
It is partially reflected, and the time taken for the reflection to return can be used to find the distance to the boundary.
21.Give two uses of ultrasound.
Medical imaging such as scans of an unborn baby, and industrial testing for cracks inside objects.
22.Why is ultrasound preferred to X-rays for scanning a fetus?
It is non-ionising, so it does not carry the risk of damaging cells.
23.What are P waves?
Longitudinal seismic waves that can travel through both solids and liquids.
24.What are S waves?
Transverse seismic waves that can travel through solids but not liquids.
25.What do S waves reveal about the Earth?
They cannot pass through the outer core, which provides evidence that it is liquid.
26.How do seismic waves show the structure of the Earth?
They refract as they pass through the interior, and the shadow zones where they are not detected reveal the size and state of the layers.
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