Chapter 5.2 Notes

5.2

Learning from Light

What are the three basic types of spectra?

Continuous, emission line, and absorption line.

Intensity

The amount of the light at each wavelength in the spectrum.

How does light tell us what things are made of?

Energy levels

Electrons in atoms have only particular amounts of energy, and not other energies in between.

Energy level transitions

An electron can rise from a low energy level to a higher one or fall from a high level to a lower one.

-The photons that produce emission lines are created when electrons fall to lower energy levels.

-Absorption lines occur when photons cause electrons to rise to higher energy levels.

-Every kind of atom, ion, and molecule produces a unique spectral "finger print".

How does light tell us the temperatures of planets and stars?

Planets, stars, rocks, and people emit thermal radiation that depends solely on temperature.

The Two Laws of Thermal Radiation

Law 1: Each square meter of a hotter object's surface emits more light at all wavelengths.

Law 2: Hotter objects emit photons with a higher average energy.

(-Hotter objects emit more total light per unit surface area and emit photons with a higher average energy.)

How does light tell us the speed of a distant object?

Doppler Effect

-Spectral lines shift to shorter wavelengths when an object is moving toward us, and to longer wavelengths when an object is moving away from us.

Blueshift

The Doppler shift of an object coming toward us.

Redshift

An object moving away from us. (Longer wavelengths of visible light are redder.)