The Electromagnetic Spectrum

Some Vocabulary• Transparent- allowing light to pass through so that

objects behind can be distinctly seen.

• Transluscent- allowing light, but not detailed shapes, to pass through

• Opaque- not able to be seen through;

Forms of Electromagnetic Radiation• Radiowaves (very long wavelength (λ), low energy, travels through atmosphere)

• Microwaves (long λ, low-medium energy, travels through atmosphere)

• Infrared (medium λ, medium energy, absorbed by CO2 – passes through O2 and N2)

• Visible Light (medium-small λ, medium energy, passes through atmosphere, blocked by most solids)

• Ultraviolet (small λ, medium-high energy, absorbed by ozone – passes through other gases)

• X-rays (small λ, high energy, passes through almost everything but metals – absorbed by ionosphere)

• Gamma rays (very small λ, very high energy, passes through almost everything - absorbed by ionosphere)

How Fast Does Light Move?

• The speed of light 300,000,000 meters per second.

• The Earth is 40,075 km in circumference.

• How long would it take a beam of light to go around the world?

How Fast Does Light Move?

• The speed of light 300,000,000 meters per second.

• The Earth is 40,075 km in circumference.

• How long would it take a beam of light to go around the world?

How long does it take to send a signal to Mars?

• On Average, the Earth is 225 million km from Mars.

• It varies from 35 million km to 400 million km.

How long does the average signal from NASA take to get to the Mars rovers?

Communicating with Mars• 300,000,000 m/sec is 300,000 km/sec

• 225,000,000 km is average distance to Mars

• 225,000,000 km ÷ 300,000 km/sec = 750 sec

• 750 sec ÷ 60 sec/min = 12.5 min each way

New Horizons• First craft to visit Pluto

• Also visited Ultima Thule

New Horizons is 6,530,000,000 km from Earth. How long does it take a signal to get from the ship?

Which Forms of Electromagnetic Radiation are Safe and Which are Dangerous?

• Electromagnetic radiation can be defined as ionizingand non-ionizing radiation.

• Radiation can only interfere with particles at the same size as the wavelengths.

We Are Bombarded by Radiation All The Time!

• Visible light, infrared, and radiowaveshit us all the time from the sun, cell towers, wifi, radio and TV stations, and the atmosphere itself.

We Are Bombarded by Radiation All The Time!

• These non-ionizing forms of radiation have wavelengths too long to interfere with molecules.

• All they can do is heat you up.

A man’s ear heated by cell phone usage

Ionizing Radiation

• These waves have enough energy and small enough wavelengths to knock electrons off the atoms to form ions.

An ion is defined as an charged atom who has lost or gained electrons

Ionizing Radiation

• Since this radiation can change molecular structure, they can damage DNA, killing the cells or causing mutations and cancer.

Ability to Penetrate

• UV radiation can only penetrate the outermost layers of the skin.

• X-rays can penetrate all soft tissues, but not the denser bone material.

• Gamma Rays can go all the way through.

Dangers of Ultraviolet Radiation

• It can directly kill your cells (why a sunburn will peel).

• It can mutate them and cause them to become permanently damaged.

• It can create pre-mature aging, liver spots, wrinkles.

Skin Cancer• Sometimes the mutations caused by UV light will

result in cancerous cells.

• These melanomas are very dangerous and can kill people!

X-Rays

• X-rays pass through low density material, but are blocked by denser material like bone or metal.

X-Rays

• This makes them useful for detecting broken bones, internal objects and for security purposes.

• But, they come with risks…

Lead Sheet for X-Rays

• Ever notice how the nurse or dentist runs out of the room when taking X-rays?

Black Box Radiation

• All matter in the universe releases energy.

• The type of energy is based on its temperature.

• Cold things only release low energy radiation like radiowaves.

• Hot things release infrared or even enter the visible light range if hot enough.

What is the Static on the Radio or Old Antenna TV sets?

Listening to Lightning on the Radio

Infrared Imaging (IR)

• Warmer things release more infrared radiation than cooler objects.

• Eventually, they can get hot enough to glow in visible light

Infrared UltravioletVisible Spectrum

550˚CHot

but not glowing Glowing red Glowing yellow Glowing white

Glowing whitish blue

1300˚C1100˚C 1500˚C

Star Colors Are Based On Their Temperatures

Star Colors Are Based On Their Temperatures

Star Colors Are Based On Their Temperatures

Thought Question: Could a Star Be So Hot, it Transmit Outside the Visible Spectrum?

• No, because even as the wavelengths shift, it still releases MORE light at every wavelength due to having more energy.