EL.2 Flashcards
Wave and particle models of light
What is the method chemists use to gain a better understanding of the origin, structure and composition of the universe?
Spectroscopy.
What scientific principle does the work of spectroscopic techniques base on?
The fact that a substance can absorb or emit electromagnetic radiation in a very characteristic way. There are many types of electromagnetic radiation and by analysing the EM waves you can identify a substance and find information about it, such as its structure and the way atoms are held together.
Describe the appearance of an absorption spectrum.
Coloured background with black lines where certain frequencies of visible light are missing.
What idea about particles in stars was used in the absorption spectra?
Particles in the chromosphere (a region outside the a starโs surface that contains ions, atoms, and small molecules) absorb some of the radiation emitted so when the light from stars were analysed certain frequencies were missing. The frequencies that were missing were absorbed by the particles in the chromosphere.
Describe the appearance of an emission spectrum.
Black background with coloured lines corresponding to the frequencies emitted.
What idea about particles in stars was used in the emission spectra?
When particles in the chromosphere absorb energy, they are raised from their ground state to a higher energy state called excited state. The particles can lose their extra energy by emitting electromagnetic radiation which is detected.
What are the two theories used to describe the behaviour of light?
The wave theory and the particle theory.
What is the relationship between frequency and wavelength of an electromagnetic wave?
They are inversely proportional. E.g. higher frequency means shorter wavelength and vice versa.
What is the equation that links speed of light, frequency and wavelength?
Speed of light (m/s) = wavelength (m) x frequency (1/s)
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What are the electromagnetic waves?
Radiowave, microwave, infrared, visible light, ultraviolet, x-ray, gamma ray.
What characteristic of a light wave is the same for all kinds of electromagnetic radiation?
The speed, c.
What is the speed of light in a vacuum?
3 x 10^8 m/s
What does the particle theory regard light as?
A stream of tiny packets of energy called photons.
What does the energy of the photon tell you about the light?
The energy of the photon tells you the position of the light in the electromagnetic spectrum.
How are the wave theory and particle theory related in a single equation?
energy of photon E (J) = Plank constant h (J/s) x frequency v (1/s)
