Waves - P6 - OCR 21st Century Science

Notes for P6

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P6 ­ The Wave Model of Radiation ­ Answers
1. Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being
2. In transverse waves, the vibrations are at right angles to the direction of travel. Light and other types of
electromagnetic radiation are transverse waves. Water waves and S waves (a type of seismic wave) are also
transverse waves.
3. Sound waves and waves in a stretched spring are longitudinal waves. P waves (a type of seismic wave) are also
longitudinal waves. In longitudinal waves, the vibrations are along the same direction as the direction of travel.
4. The frequency of a wave is the number of waves produced by a source each second. It is also the number of
waves that pass a certain point each second. The unit of frequency is the hertz (Hz).
5. The wavelength of a wave is the distance between a point on
one wave and the same point on the next wave. It is often
easiest to measure this from the crest of one wave to the crest
of the next wave, but it doesn't matter where as long as it is the
same point in each wave.
6. As waves travel, they set up patterns of disturbance. The
amplitude of a wave is its maximum disturbance from its undisturbed position. Take care: the amplitude is not
the distance between the top and bottom of a wave. It is the distance from the middle to the top.
7. The speed of a wave is generally independent of its frequency or amplitude.
8. Sound
waves reflect from surfaces. Remember that they
behave just like water waves in a ripple tank. The angle
of incidence equals the angle of reflection. Smooth
surfaces produce strong echoes when sound waves hit
them, and they can act as mirrors when light waves hit
them. The waves are reflected uniformly and light can
form images. Rough surfaces scatter sound and light in all directions. However, each tiny bit of the surface still
follows the rule that the angle of incidence equals the angle of reflection.
9. The waves can:
Be focused to a point, for example sunlight reflected off a concave telescope mirror.
Appear to come from a point behind the mirror, for example a looking glass.
10. Sound waves and light waves change speed when they pass
across the boundary between two substances with different

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This causes them to change direction and this effect is called refraction.
11. Beyond a certain angle, called the critical angle, all the waves reflect back into the glass. We say that they are
totally internally reflected. All light waves, which hit the surface beyond this critical angle, are effectively
trapped. The critical angle for most glass is about 42 °.
12. An optical fibre is a thin rod of high-quality glass.
Very little light is absorbed by the glass.…read more


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