chapter 5: Radiation and the spectra

Light as a wave

Wavelength, amplitude, frequency and speed

Speed of light related to wavelength and frequency

$$c=\lambda\cdot f$$

C = 3 × 10^8 m/s

Key point (light as wave)

Wavelength and frequency are inversely proportional; one goes up the other goes down

Light as a particle

Photon, travels at the speed of light

$$E=hf$$

E = 1/wavelength

h = Planck constant

Higher frequency or shorter wavelength are more energy

Key point (light as particle)

Energy and frequency are directly proportional, one goes up the other goes up

Electromagnetic spectrum (short to long)

gamma rays

X-rays

Ultraviolet

Viable light

Infrared

Microwave

Radio

Wien law

$$\lambda=\frac{3\cdot10^6}{T}K=\frac{1}{T}$$

Hot objects glow and emit continuous spectrum of light but their peak wavelength depends on temperature

T= temperature of body

Shorter = hotter

Longer = colder

Hotter = more energy and brighter

Key point ( peak wavelength)

Peak wavelength and temperature are inversely proportional, one goes up the other goes down

Four ways light interacts with matter

Emission: matter releases energy as light

Absorption: matter takes energy from light

Transmission: matter allows light to pass through it

Reflection: matter repels light in another direction

From an objects spectrum

Composition: from spectral lines: emission lines or absorption lines

Temperature: continuous spectra, Wien law

Atomic structure

Nucleus contains protons and neutrons

Electrons outside the nucleus are only allowed to be in certain discrete energy levels

Electrons jumping up in energy: absorption

Electrons down in energy: emission

Key point ( electrons)

Different atoms have different energy levels, so the associated spectral lines form a unique fingerprints for each atom

Three types of spectra

Emission: thin and hot gas: gas glows in a specific colors. Colors represent electrons falling down energy levels (sharp peaks)

Continuous: hot solids: continuous rainbow of light

Absorption: hot object through cool gas: dark lines on top of a rainbow (sharp dips)

Spectrum of a planet

Typically has two bumps:

Reflected sunlight/starlight: peak in visible light range

Light emitted from plate via thermal radiation: peak in infrared light range

Surface temp without greenhouse effect

Distance from sun: closer planets are generally hotter

Reflectivity: more reflectivity colder, less reflectivity hotter

Hotter vs Colder colors

Hotter, peak in blue

Colder, peak in red