- Which waves need a medium to travel, which not?
- What is the wavelength of a wave?
- What is the speed of a light wave?
- Explain the difference between wavelenght and frequency of a wave.

- Waves which need a medium to travel: sound, water, seismic

Waves which need no medium to travel: electromagnetic waves - The wavelength of a wave: The distance between to adjacent identical points in a wave.
- speed of a light wave: 300,000,000 m/s
- difference between wavelength and frequency: The frequency is the number of wave cycles per second.

Calculate the speed of different waves.

- sound waves
- Wi-fi waves
- light waves
- water waves
- seismic waves

- sound waves: in air: $c=340\: m/s$, in water: $c=1500\: m/s$
- Wi-fi waves: $c=300\cdot 10^6\: m/s$
- light waves: $c=300\cdot 10^6\: m/s$
- water waves: depends on depth of water and the wavelength: for example with $\lambda=340\: m$ we can have $c=23\: m/s$.
- seismic waves: $c=2000-8000\: m/s$

The time-displacement-diagram shows the sound waves produced by two loudspeakers A and B.

- Calculate the frequency
*f*of the waves. - Determine the phase shift between the two waves.
- State the type of wave produced by the speakers.
- Reason which loudspeaker produces a louder sound.
- Calculate the speed of the sound waves.

- frequency
*f*of the waves: $f=\frac{1}{T}=\frac{1}{2\:ms}=500\:Hz$ - phase shift between the two waves: $\varphi=90\: °$
- Sound waves are longitudinal waves
- The displacement or amplitude of loudspeaker A is larger. Therefore speaker A produces a louder sound.
- wavelength of the sound waves: $\lambda=\frac{c}{f}=\frac{340\:m/s}{500\:Hz}=68\: cm$

Tsunamis do threaten many costal regions.

275,000 people lost their lives by the Tsunami occured 2004 in the Indian ocean.

- Find out the speed and wavelength of this Tsunami wave.
- What was the reason for the huge Tsunami?
- Find out the vertical displacement of a Tsunami wave.
- State why the height in shallow water increases dramatically.

- speed: $c=200\:ms^{-1}$, wavelength: $\lambda=100\:km$
- At the coast of Sumatra the see bed moved 15 m vertically over a length of 1500 km.
- amplitude: $\hat{y}=1\: m$
- In shallow water the wave slows down, so the tail of the wave catches up the front and mounts up to increased height.

wavelength $\lambda$ | distance between two maxima of a wave |

frequency $f$ | number of oscillations per second |

speed of light $c$ | rate at which light travels $c=300\cdot 10^6 $ m/s |

amplitude | intensity of a wave |

displacement | an object's change in position |

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