# Light and Atoms Chapter 3.

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Light and Atoms Chapter 3

Properties of Light It does not need a medium (substance to travel through) need air or water to travel through. There is no sound in space

Manifestations of Light
Light can be explained by models 1. Light as a _______ wave – A wave consisting of alternating electric and magnetic energy. Ex. Visible light, color depends on wavelength. 2. Light as a ____________. Light is also considered a subatomic particle that in empty space travels in a straight line at the speed of light. – A particle of visible light or other electromagnetic radiation.

When to use a specific model?
Scientist use whichever model best explains the properties of light at any given time. When they explain how a lens focuses light they use the wave model. When they want to explain how light bounces off of a mirror they use the particle model. Light is described as having ____________ _____________.

Light and color _______________ – The portion of electromagnetic radiation that the human eye is sensitive to. Red, orange, yellow, green, blue, indigo, and violet The difference in color is due to the difference in wavelength. Wavelength - Wavelengths of light are measured in nanometers.

Various Laws related to light
Wien’s law Remember higher energy light has higher frequency and shorter wavelengths.

Various laws related to light
Stefan’s law – When Stefan’s law and Wein’s law are both applied we are able to determine that as temperature increases so does the intensity of light

Various laws related to light
Kirchhoff determined that there are 3 different kinds of spectra. – light we see via a prism – light we see emitted from a source. Shows lines from the wavelengths emitted by a heated element. – spectra of light with black lines (light that was absorbed by a material or gas) Kirchhoff’s law –

The Doppler Shift If a source of light is in motion, its spectral lines shift to new wavelengths. The Doppler shift results in the

Directions of the Doppler Shift
The shift is an increase in the wavelength if the source and observer move apart. The shift is a decrease in wavelength if the source and observer approach each other. The Doppler shift results in a redshift or blueshift.

Redshift A shift in the wavelength of electromagnetic radiation to a longer wavelength. For visible light this implies a shift toward the red end of the spectrum. Redshifts occur when the source moves ________ from the observer or when the observer moves away from the source. If a star moves away from the Earth then its light will appear more red.

Blueshift A shift in the wavelength of electromagnetic radiation to a shorter wavelength. For the visible light, this implies a shift toward the blue end of the spectrum. The shift can be caused by the motion of the source of radiation ____________ the observer or by the motion of the observer toward the source. A star moving ________ the Earth will exhibit a blueshift.

Our atmosphere also bends light waves so that most stars have a similar appearance regardless of what spectra of light they may be emitting.

Blackbodies A blackbody is an object that absorbs all light that falls on it. No electromagnetic radiation passes through it and none is reflected. Because no light is reflected or transmitted, the object appears black when it is cold.

Blackbodies (Continued)
When a blackbody is “hot”, it is a source of thermal radiation. Incandescent light bulbs are an example of black bodies. The Sun is also an example of a Blackbody When a Blackbody is hot enough to emit radiation, it is termed blackbody radiation When hot gases emit radiation it is termed emission-line radiation

Blackbody Radiation At room temperature, black bodies emit infrared light. As temperature increases past a few hundred degrees Celsius, black bodies start to emit at visible wavelengths of light Blackbody radiation in the visible spectra ranges from red, through orange, yellow, and white before ending up at blue, Beyond blue light, the emission includes increasing amounts of ultraviolet light.

Parts of the Atom – Positively charged particles found in the nucleus of an atom. The identity of an atom is determined by the number of protons found in the nucleus. – Neutrally charged particles found in the nucleus of an atom. – Negatively charged particles spinning around the nucleus of the atom.

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