Light and Atoms

1. Light and Atoms Chapter 3

2. 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

3. 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.

4. 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 ____________ _____________.

5. 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.

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

7. 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

8. 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 –

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

10. 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.

11. 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.

12. 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.

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

14. 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.

15. 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

16. 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.

17. 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.