The Nature of LightThe Nature of Light

Let’s Review…Let’s Review…

What are some of the differences What are some of the differences between sound waves and light between sound waves and light waves?waves?

Sound WavesSound Waves

Mechanical waveMechanical wave Longitudinal waveLongitudinal wave Requires a medium Requires a medium

to travel throughto travel through Created by Created by

vibrationsvibrations Speed of Sound:Speed of Sound: 343 m/s343 m/s

Light WavesLight Waves

Electromagnetic Electromagnetic wavewave

Transverse waveTransverse wave DOES NOT require a DOES NOT require a

medium to travel medium to travel throughthrough

Created by vibration Created by vibration of electrically of electrically charged particlescharged particles

Speed of Light:Speed of Light:300,000,000 300,000,000

m/sm/s

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Why can you see your reflection in a Why can you see your reflection in a mirror and not off of a brick wall?mirror and not off of a brick wall?

Interactions of Light WavesInteractions of Light Waves

What is reflection?What is reflection?

Why does light bounce differently off Why does light bounce differently off of different objects?of different objects?

How can you change the way a ball How can you change the way a ball will go when you bounce it?will go when you bounce it?

Law of ReflectionLaw of Reflection

The The Law of ReflectionLaw of Reflection states that states that the angle of incidence is equal to the the angle of incidence is equal to the angle of reflection.angle of reflection.

Light Source

Why does a flashlight appear Why does a flashlight appear brighter when you are near it?brighter when you are near it?

Absorption…….what does this word Absorption…….what does this word mean to youmean to you

Just like a sponge soaking up water, Just like a sponge soaking up water, particles of matter can absorb the particles of matter can absorb the energy from waves of light. When energy from waves of light. When there is enough matter (including air) there is enough matter (including air) to absorb it, there is none left for us to absorb it, there is none left for us to see.to see.

In addition to being reflected In addition to being reflected and absorbed….light can bendand absorbed….light can bend

RefractionRefraction and and diffractiondiffraction are two are two different types of bending…..different types of bending…..

Even though it is bending, the light is Even though it is bending, the light is passing THROUGH an object…this is passing THROUGH an object…this is called called transmissiontransmission..

RefractionRefraction

• Light bends when it Light bends when it travels from one travels from one medium to another medium to another (changes speed)(changes speed)

DiffractionDiffraction

• Light bending to go Light bending to go around a corner or around a corner or through an through an opening.opening.

SummarySummary

What are the 3 main things that light What are the 3 main things that light waves do when they interact with waves do when they interact with matter?matter?

Which of these occurs as light makes Which of these occurs as light makes it way from the sun to your eyes?it way from the sun to your eyes?

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Calculate the time it takes for light Calculate the time it takes for light from the sun to reach Mercury. from the sun to reach Mercury. Mercury is 54,900,000,000 meters Mercury is 54,900,000,000 meters away from the sun.away from the sun.

Hint: remember the formula for Hint: remember the formula for speedspeed

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speed = distance/timespeed = distance/time

time = distance/speedtime = distance/speed

time = time = 54,900,000,000 m 54,900,000,000 m = 183 = 183 secondsseconds

300,000,000 m/s300,000,000 m/s

Just to review…Just to review…

What are 3 things that can happen What are 3 things that can happen to light when it strikes an object?to light when it strikes an object?

1.1. ReflectReflect

2.2. AbsorbAbsorb

3.3. Transmit (bend, but go through)Transmit (bend, but go through)

The combination of reflecting, The combination of reflecting, absorbing and transmission absorbing and transmission

determines what you see when determines what you see when you look at an objectyou look at an object

TransparentTransparent

An object is transparent (or see An object is transparent (or see through) when light is easily able to through) when light is easily able to pass through it.pass through it.

TranslucentTranslucent

When some light is scattered as it When some light is scattered as it tries to pass through an object, it tries to pass through an object, it causes a blurry appearance…this is causes a blurry appearance…this is translucent….translucent….

OpaqueOpaque

If an object absorbs some colors and If an object absorbs some colors and reflects the rest, we say it is reflects the rest, we say it is opaque….which means you can’t see opaque….which means you can’t see through itthrough it

The color reflected back would be the The color reflected back would be the color that we see….all others would color that we see….all others would be abosorbed…be abosorbed…

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What are 3 ways that light can What are 3 ways that light can interact with other objects?interact with other objects?

What are 3 ways that those What are 3 ways that those interactions can cause objects to interactions can cause objects to appear?appear?

Vocabulary QuizVocabulary Quiz

LightLight White LightWhite Light TransparentTransparent TranslucentTranslucent OpaqueOpaque

LensLens MirrorMirror PrismPrism Electromagnetic Electromagnetic

WaveWave Electromagnetic Electromagnetic

SpectrumSpectrum

Electromagnetic SpectrumElectromagnetic Spectrum

EM energy is created by vibrations EM energy is created by vibrations that carry energy….each EM wave that carry energy….each EM wave emits a different energy level.emits a different energy level.

All of these waves together are All of these waves together are known as the known as the electromagnetic electromagnetic spectrumspectrum..

Radio WavesRadio Waves

Lowest energy of light – longest Lowest energy of light – longest wavelength – used for wavelength – used for communication since they travel long communication since they travel long distances… distances…

(Radio waves are NOT sound (Radio waves are NOT sound waves…they only become sound waves…they only become sound when they are received by a radio when they are received by a radio and changed into sound) and changed into sound)

MicrowavesMicrowaves

Used for communication, weather Used for communication, weather radar and cooking foodradar and cooking food

InfraredInfrared

Waves in the form of heat…Waves in the form of heat…

Visible LightVisible Light

Range of wavelengths that the Range of wavelengths that the human eye can detect….human eye can detect….

Red has longest wavelength

Violet has the shortest wavelength

Wavelength and Frequency of Visible Light

Indigo has a wavelength of 445nm and 673 THz

Indigo has a wavelength of 445nm and 673 THzA THZ is a terahertz which is 10 12 Hertz

Ultraviolet LightUltraviolet Light

Wavelengths that are just “beyond Wavelengths that are just “beyond violet” on the spectrumviolet” on the spectrum

Carry more energy than visible lightCarry more energy than visible light Will cause skin damageWill cause skin damage

X-RaysX-Rays

Used for imaging – can travel well Used for imaging – can travel well through soft substances….not as well through soft substances….not as well through dense materialsthrough dense materials

Gamma RaysGamma Rays

Gamma Rays – highest energy light – Gamma Rays – highest energy light – shortest wavelength - damaging to shortest wavelength - damaging to cells – used to sterilize medical cells – used to sterilize medical equipment –equipment –

Used to treat cancerUsed to treat cancer