Study of Light Study of Atoms - Linn–Benton Community ...cf.linnbenton.edu/mathsci/physci/rajabza/upload/7_Light1.pdf · Intro to Galaxies Light and Atoms - I 19 Rule #3: If a continuous

Intro to Galaxies Light and Atoms - I 1

Astrophysics

Study of Light

Study of Atoms


Atomic Physics

elements: substances which cannot be broken

down into simpler substances

atom : smallest unit of an element that

displays the chemical properties

of the element

compounds: substances made up of two or more

elements

molecule: smallest unit of a compound that

still has the chemical properties of the

compound


Model of an Atom

dense nucleus of

neutrons and protons

(massive particles) rapidly moving

electron (low

mass)

proton: positively charged

electron: negatively charged

neutron: no charge


Hydrogen Atom

most common element

in the Universe !

e-

p+ nucleus, size of a marble

electron is 1 km away


Number of protons in an atom is

what makes one element

different from another

Hydrogen - 1 protons

Helium - 2 protons

Carbon - 6 protons

Electrons determine the chemical

properties of atoms.


neutral atoms: electrons = protons

isotopes: same element with different

number of neutrons

ions: electrons = protons

e.g. an atom loses an electron

- positively charged

- called a positive ion


Light

spectroscopy: art of breaking up light into its

component colors

spectrum: sequence of colors resulting from

dispersing light through a prism, a grating

or a raindrop

V R O Y G. B I


continuous spectrum: broad bands of color

with no breaks, no separations

line spectrum:

• a bright sharp line (or lines) in a

particular color

• a dark line where light is missing

in a particular color


emission spectrum: bright line spectrum

absorption spectrum: continuous spectrum

with superimposed dark lines

spectroscope: an instrument for observing

details in a spectrum


Experiments • neon sign

bright emission lines in red

• mercury street light

bright emission lines in yellow & green

• sodium street light

bright emission lines in yellow

• salt in a colorless flame

series of bright emission lines, a pair

in yellow


Each chemical element displays

a unique arrangement of bright

lines when excited (i.e. heated)

in a gaseous state.


Look at sunlight (not directly, but reflected)

We see dark lines imposed on a continuous

spectrum, specifically a pair in the

yellow part of the spectrum.

A match for the pair of bright yellow lines

seen in a sodium flame!

This tells us there is sodium present in the Sun !


Spectrum of the Sun

Kaufmann & Comins 4/e


Spectrum of the Sun

Zeilik 6/e


Zeilik 6/e

Solar Spectrum


Zeilik 6/e

Spectrum of Star, Canopus


Kirchhoff’s Rules

Rule #1:

A hot opaque solid, liquid or

highly compressed gas, emits

a continuous spectrum.

Kaufmann & Comin 4/e


Rule #2:

A hot, transparent

gas produces a

spectrum

of bright lines

emission lines).

The number and

color of the lines

depend on which

elements are in the gas.



Rule #3:

If a continuous spectrum

(from a hot, opaque solid, liquid or gas)

passes through a transparent (i.e. cooler) gas,

the cooler gas causes the appearance of dark

lines (absorption lines) in the continuous

spectrum.

The number of color of lines depend on which

elements are present in the cooler gas.





Energy

energy: ability to do work

conservation of energy:

total energy of an isolated system remains

constant regardless of what changes

happen inside the system


kinetic energy: energy of motion

KE = 1/2 m v2

depends on mass and velocity

potential energy: energy that is stored due

to an applied force

- potential to do work

- fuels, batteries

gravitational potential energy:

energy of position

radiative energy: energy carried by light


Conservation of Energy

Energy cannot be created or

destroyed; it may be transformed

but the total does not change.


Light and Electromagnetic

Radiation

waves: undulations with a regular timing


frequency: number of waves per second

wavelength: distance from one peak to

another peak

wavelength


velocity: how fast the wave is traveling

and in what direction

No matter moves with waves; wave carries

energy but does not transport materials.


Fundamental Rule for Light

f l = v f = frequency

l = wavelength

v = velocity

The speed of light is called, c

for light the rule is:

f l = c c = 300,000 km/sec


f l = c

Given that the speed of light is constant:

change in wavelength change in frequency

decreases

increases decrease the frequency, wavelength ?????

increase the frequency, wavelength ?????

an inverse relationship


Electromagnetic Spectrum

complete range of wavelengths of

EM radiation gamma rays

x-rays

ultraviolet rays (UV)

visible

infrared (IR)

microwave

radio waves


The ElectroMagnetic Spectrum Kaufmann & Comin 4/e




Ground-based

vs Hubble

Light Pollution

Tucson 1959

vs 1980



USA at Night from Space

APOD


angstrom: , unit of measure for wavelength

1 = 10-10 m

hertz: unit of measure for frequency,

number of cycles per second

visible light - red 7000

violet 4000


Why the pattern of light

and dark lines ?

. . . stay tuned

Documents

Study of Light Study of Atoms - Linn–Benton Community ...cf.linnbenton.edu/mathsci/physci/rajabza/upload/7_Light1.pdf · Intro to Galaxies Light and Atoms - I 19 Rule #3: If a continuous