Intro to light - Flame Test

• Can be used to identify elements.

• Energy (heat) is used to excite electrons in an atom.

• Electrons temporarily move from ground state (where they prefer to be) to excited state (a high energy level).

• As electron returns to ground state, atom emits energy in the form of light.

Gulp!!!Shake!!Burp!!Photon

Electromagnetic Radiation(light)

• Produced by changing electric and magnetic fields

• Can be thought of as both a particle and a wave (wave-particle duality)

• Does NOT require a medium• Transverse

Mechanical waves

Electromagnetic waves

Read pgs. 500, 532, 533

HOMEWORK

Electromagnetic Waves

Homework Assignment:

•Read pg. 500, 532, 533

•Make a double bubble map to compare and contrast electromagnetic waves to mechanical waves.

Light as a Wave

• When we treat light as a wave, it has the properties of any other wave:

1. Wavelength2. Frequency3. Speed

• These properties are related just like they are with mechanical waves.

What is the formula?

Speed = Wavelength x Frequency

• The Sun is the source of EM radiation on Earth

• Speed remains the same: all EM waves travel at the speed of light:

3.00 x 108 m/s

Electromagnetic RADiation

Practice Problems

1. What is the wavelength of an electromagnetic wave that has a frequency of 4.03x1014 Hz?

2. What is the frequency of an electromagnetic wave that has a wavelength of 3 m?

Electromagnetic Spectrum

• When we think of light as a wave, we discover that electromagnetic radiation (light) can come in many forms. These forms depend on the wavelength and frequency of the light.

• Electromagnetic waves of different frequency/wavelength fall onto different places on the electromagnetic spectrum.

Electromagnetic Spectrum

Left to Right: wavelength decreases, frequency increases

Electromagnetic Spectrum

Radio Waves

• Used in radio and television transmission.

microWaves

• Used in microwave appliances

• Radar waves are also a form of microwaves

Infared waves

• Show the amount of thermal energy (heat) a particular object has.

• Heat or Night Vision

Visible Light waves

• Waves our eyes are capable of seeing

ROYGB IV

Ultraviolet Waves

• First potentially harmful form of EM radiation

• Overexposure can lead to skin cancer

X-Rays

• Used in the medical field to look inside the human body

Gamma Rays

• Highest energy form of EM radiation• Hardest radiation to be protected

from• Used in treatment of cancer

(radiationtreatment)

What is giving off radiation?

• By studying and displaying the em radiation given off by stars, scientists can determine the chemical composition of those stars among other things.

Spectrum/Spectra

Spectrum to made a display out of something

In astronomy, we display radiation using spectroscopes (bend light to see various wavelengths being emitted)

Each element produces a set of characteristic emission lines

• From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star. The spectral line also can tell us about any magnetic field of the star. The width of the line can tell us how fast the material is moving. We can learn about winds in stars from this. If the lines shift back and forth we can learn that the star may be orbiting another star. We can estimate the mass and size of the star from this. If the lines grow and fade in strength we can learn about the physical changes in the star. Spectral information can also tell us about material around stars. This material may be falling onto the star from a doughnut-shaped disk around the star called an accretion disk. These disks often form around a neutron star or black hole. The light from the stuff between the stars allows astronomers to study the interstellar medium (ISM). This tells us what type of stuff fills the space between the stars. Space is not empty! There is lots of gas and dust between the stars. Spectroscopy is one of the fundamental tools which scientists use to study the Universe.

Spectra

ContinuousA luminous solid or liquid

emits a continuous spectrum of all

wavelengths. It has no lines in it.

Discrete

EmissionWhen hot gas is emitted its own light

AbsorbtionWhen light from a brigher source is shone through it

Signatures of elements

Sun Spectrum