## Wave motion | waves | physics | fuseschool

Water molecules are made up of oxygen atoms; does this mean that water, H2O, and oxygen O2 have similar properties? No, compounds are not interchangeable with the elements from which they are formed.
You have a good risk of dying if you ingest metallic sodium or inhale cholrine gas. Allow these two elements to react, and you can then sprinkle the compound on your popcorn for a better flavor. What really is going on? Sodium chloride bears no resemblance to sodium or cholrine.

## Why does light bend when it enters glass?

Explanation: For light, the Doppler shift equation is, where f is the source frequency, f’ is the observed frequency, v is the relative velocity between the source and the observer, and c is the speed of light.
Because v is positive as the source and observer move closer together, the observed frequency is greater than the source frequency. Since shorter wavelengths are associated with higher frequency, visible light is moved towards the blue end of the spectrum.
An 880Hz siren is emitted by a fire truck. The pitch of the truck as it hits an obeserver on the sidewalk is 950Hz. After the truck has passed and is going on, what pitch does he hear? Assume that the truck’s speed remains constant and that the sound velocity in air is 340m/s.
Explanation: The Doppler effect equation is, with the + sign indicating that the source and observer are moving further apart and the – sign indicating that they are moving closer together.
In these equations, v is the sound speed, which is 340m/s, is the source’s frequency, is the observer’s frequency, and is the relative velocity between the source and the observer.

### Transverse & longitudinal waves | waves | physics

Gillian Isoardi has disclosed no relevant affiliations beyond their academic appointment, and does not work for, consult, own shares in, or receive support from any corporation or organization that would benefit from this article.
When an ambulance drives by with its siren blaring, you can hear the tone of the siren change: it sounds higher as it approaches you than when it is heading away from you. A typical physical demonstration of the Doppler effect is this transition.
When there is relative motion between the wave source and the observer, the Doppler effect describes the change in the observed frequency of a wave. Christian Johann Doppler, an Austrian mathematician and physicist, suggested it in 1842. Doppler observed distant stars and described how the color of starlight changed as the star moved.
To understand why the Doppler effect happens, we must first understand a few fundamental characteristics of wave motion. Waves can take many forms: ripples on a pond’s surface, noises (like the siren above), illumination, and earthquake tremors are all examples of periodic wave motion.

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What is the Stokes Shift, and what does it mean?

### Label & draw transersve waves: amplitude, frequency

The Stokes Change is the spectral shift from higher energy incident light to lower energy scattered or emitted light after contact with a sample, named after Irish physicist George Gabriel Stokes. This article introduces the Stokes Change, which is a key principle in both fluorescence and Raman spectroscopy.
G. G. Stokes researched the properties of what we now call fluorescence extensively in the mid-nineteenth century, focusing on how fluorescent light differed from incident light. In 1852, he presented his findings to the Royal Society of London, titled “On the Change of the Refrangibility of Light.” 1 In this work, he stated:1,2 “There appears to be one universal law relating to internal dispersion [fluorescence]: when the refrangibility [the degree of refraction – inversely proportional to wavelength] of light is modified by dispersion, it is always lowered [shifted to longer wavelengths].”
The fluorescence emission occurs at a longer wavelength than the incident light, according to Stokes’ Law. The Stokes transition, which occurs when the absorption and fluorescence spectra shift to longer wavelengths, is named after him.