Chapter 17 - LightChapter 17 - Light

An electromagnetic wave is composed of An electromagnetic wave is composed of electric and magnetic fields that are electric and magnetic fields that are vibrating perpendicular to each other. vibrating perpendicular to each other.

What is polarized light?What is polarized light? When light goes through a polarized filter only When light goes through a polarized filter only

vibrations of one direction are allowed through.vibrations of one direction are allowed through. Polarized light – light that is vibrating only in one direction.Polarized light – light that is vibrating only in one direction.

Light acts like both a Light acts like both a particle and a waveparticle and a wave

Photoelectric effect – Photoelectric effect – when light “particles” when light “particles” knock electrons off of knock electrons off of a surface.a surface.

Photon – a particle of Photon – a particle of lightlight

Radio wavesRadio waves – generated and absorbed by electrons pulsing – generated and absorbed by electrons pulsing back and forth along a wire (low energy wave)back and forth along a wire (low energy wave)

Long infrared wavesLong infrared waves – used in some communications (cell phones) – used in some communications (cell phones) Short infrared (heat waves)Short infrared (heat waves) – produced and absorbed by – produced and absorbed by

molecular vibrations, produced in microwave ovens.molecular vibrations, produced in microwave ovens.

Visible lightVisible light – created and absorbed by electrons dropping down – created and absorbed by electrons dropping down energy levels. The difference in energy of the energy levels energy levels. The difference in energy of the energy levels corresponds to the wavelength of light emitted.corresponds to the wavelength of light emitted.

Ultraviolet lightUltraviolet light – (beyond violet) (black light) cause sunburn and – (beyond violet) (black light) cause sunburn and skin cancer, helps skin provide vitamin Dskin cancer, helps skin provide vitamin D

X-raysX-rays – penetrated the body, absorbed by dense tissue – penetrated the body, absorbed by dense tissue (bone). Will darken a photographic plate.(bone). Will darken a photographic plate.

Gamma raysGamma rays – comes from all regions of space, like tiny – comes from all regions of space, like tiny bullets passing through body. Used to help treat cancer.bullets passing through body. Used to help treat cancer.

All electromagnetic waves travel the All electromagnetic waves travel the same speed but they all have different same speed but they all have different frequency and wavelength.frequency and wavelength.

What is the relationship between What is the relationship between wavelength and frequency?wavelength and frequency?

The higher the frequency, the shorter the The higher the frequency, the shorter the wavelengthwavelength

The lower the frequency, the longer the The lower the frequency, the longer the wavelength.wavelength.

The longer the wavelength the lower the energyThe longer the wavelength the lower the energy

What is radar? How does radar work?What is radar? How does radar work? Radio detection and ranging is done by Radio detection and ranging is done by

sending a pulse of radio waves. The sending a pulse of radio waves. The time it takes for them to return gives time it takes for them to return gives the distance to the object.the distance to the object.

The change in frequency as the waves The change in frequency as the waves bounce off the object can be used to bounce off the object can be used to determine how fast the object is going.determine how fast the object is going.

The police radar gun uses the Doppler The police radar gun uses the Doppler effect to determine your speed.effect to determine your speed.

What is Magnetic What is Magnetic Resonance Imaging (MRI)?Resonance Imaging (MRI)?

A short burst of radio A short burst of radio waves, along with a strong waves, along with a strong magnetic field cause a magnetic field cause a person’s atoms to line up person’s atoms to line up with the magnetic field.with the magnetic field.

The atoms return to a The atoms return to a random arrangement at random arrangement at different rates and this is different rates and this is used to give an image of used to give an image of soft tissues such as the soft tissues such as the brain.brain.

Infrared rays and thermogramsInfrared rays and thermograms Infrared cameras and thermograms Infrared cameras and thermograms

allow us to see heat radiation. One allow us to see heat radiation. One application is determining areas of application is determining areas of greatest heat loss in homes.greatest heat loss in homes.

Incandescent lightIncandescent light Incandescent lights have a tungsten Incandescent lights have a tungsten

filament that gets “white hot”filament that gets “white hot”Most of the energy given off is heat Most of the energy given off is heat

radiation (less than 10% efficient)radiation (less than 10% efficient)

How do fluorescent lights work?How do fluorescent lights work? Ultraviolet light is created as an electric Ultraviolet light is created as an electric

current passes through a vaporcurrent passes through a vapor The inside of the light is coated with a The inside of the light is coated with a

phosphor which glows when hit with U.V. lightphosphor which glows when hit with U.V. light They are more efficient than incandescent lights.They are more efficient than incandescent lights.

Sea shells under black fluorescent light

Bioluminescence – what is it? Bioluminescence – what is it? A chemical reaction within an organism produces A chemical reaction within an organism produces

light (firefly).light (firefly).

Artificial bioluminescence created by genetic engineering in a tobacco plant

AM and FM waves, what are they? AM and FM waves, what are they? How are they different?How are they different?A.M. : Amplitude modulation – the amplitude A.M. : Amplitude modulation – the amplitude

of a wave is changed to carry information.of a wave is changed to carry information.F.M. : Frequency modulation – the F.M. : Frequency modulation – the

frequency is modulated to carry information.frequency is modulated to carry information.