EM waves do not need a medium to travel through

EM waves are transverse waves

All EM waves travel at the speed of light = 3.00 x 108 m/s So, if they all travel at the same speed, how

are they different? Their energies are different!

Higher frequency = Higher Energy PRACTICAL APPLICATIONS of EM WAVES????

Backscatter X-ray full body scans:

- lower energy X-rays

- go through clothing, reflect off skin

- images with small details results,

like nonmetallic weapons & explosives

Millimeter Wave full body scans:

- millimeter wave technology

- have wavelengths of about a millimeter

- are shortest wavelength radio waves & just longer than IR waves

- ordinary clothing is transparent to millimeter wavelength radio waves, but flesh is not

- goes through clothing to reveal weapons or explosives Physics and Airport Security: How a TSA Full Body Scan Works http://www.suite101.com/content/physics-and-airport-security-how-a-tsa-full-body-scan-works-a235650#ixzz17jM4qBH5

EM Spectrum in the Airport… Full Body scans?!?!

People are protesting…

“invasion of privacy”

x-rays

UV

IR

Microwaves

Radar Radio waves

TV

FM

Visible Light

700 nm 400 nm

γ rays

-High Frequency

-High Energy

- Short Wavelength

-Low Frequency

- Low Energy

- Long Wavelength

Section Review

pg. 365

# 1-5 (due now)

and EM worksheet (due today or tomorrow)

Due to it’s wave-like nature, light has different properties when encountering a medium:

1. Interference

2. Reflection

3. Diffraction

4. Refraction

1. When food cooks in the microwave the food gets hot, but the inside of the microwave does not… why?

2. The EM waves with wavelengths slightly longer than visible light are __________________.

3. EM waves _________________________. How do you know?

a. are compressional waves b. must have a medium

c. are transverse waves

4. EM radiation with the shortest wavelength is ____________________. Longest λ?? ______________________

5. Television uses __________ to transmit signals.

a. microwaves c. visible light waves

b. infrared waves d. radio waves

6. How do we know EM waves exist if we can’t see them?

• If we can’t see Electromagnetic Waves… how do we know they are there?????

• How do Microwaves work??

• Can we calculate the speed at which microwaves travel???? – How could we?

– What equation

do we need?

A. Waves can interfere with one another. Can be constructive or destructive.

1. Constructive: crests of waves combine to create larger waves (sound waves get louder)

– Also happens with troughs, compressions, and rarefactions

2. Destructive: crests interfere with troughs to lessen the displacement of each (cancel each other out, sounds get softer)

– Compressions can also interfere with rarefactions to lessen their displacement

Obeys the “Law of Reflection”

– “The angle of incidence is equal to the angle of reflection.”

A. Angle of incidence: angle between the incident ray and a line normal (perpendicular) to the surface at the point where light strikes

B. Angle of reflection:

angle between the reflected ray and the normal line

1. Light strikes cat’s face and reflected into mirror

2. Light then reflects off the mirror into eyes

LIGHT

Diffraction: bending around a barrier or the edges of an opening

1. light waves with longer wavelengths diffract more easily than smaller wavelengths

2. light waves can diffract to produce interference patterns

Refraction: waves change direction as they enter a medium & begin to travel at a different speed

The illusion comes

from the fact that our

eye doesn't know that

the light has been

refracted when it

comes from water into

air, and so thinks that

it has originated from

a point closer to the

surface

When light

enters a

more

dense

medium

from one

less

dense, it

bends!

As light enters a prism, it slows and refracts. As it exits, it speeds back up.

Prisms create “rainbows” because the different wavelengths of light slow at different rates and bend at

different angles

Convex or Converging Lens: microscopes, magnifying glasses, and glasses

Concave or Diverging Lens:

LAB: Name that Wave Behavior!

• Rotate through each station and perform the activity

• Determine which type of wave behavior you see occurring!

• You can write on the lab sheet

• Wait to be rotated

• Answer all questions at the bottom!

1. List the 4 behaviors of light waves we talked about yesterday.

2. A prism creates a rainbow by the process of ___________________.

3. Waves bending around corners or passing through openings are examples of _________________.

4. You can see yourself in a mirror because of _____________________.

5. Explain the process in #4.

6. Why does it sometimes look like there is water on the road on a hot day, but the road is really dry?

Diffraction, interference, refraction & reflection

Refraction – bends the light as it hits the new medium

diffraction

reflection

Light hits your face, reflects to the mirror, & then into your eyes

Really hot air above road has different density than the rest of the air, so it REFLECTS & REFRACTS light differently making it look wet!

The Doppler Effect

Shift in frequency and pitch due to the changing motion of an observer or wave source

The Doppler shift can occur:

- As a person moves toward sound source or the source moves toward the person… and vice versa (moving away)

Doppler Effect and Pitch

As the wave source approaches the observer, the observer perceives a higher frequency than the sound is really producing. Why? Shorter wavelengths & higher frequency when in front

of a moving source = higher pitch

When the wave source is moving away from the observer, the perceived frequency is lower than really produced. Why? – As the sound moves away, the wavelengths increase = Low frequency, Low pitch

Doppler Effect in Review… 1. Why does the Doppler Effect occur ?

2. Specifically, what does the Doppler Effect do to sound and the sound wave?

3. Does the speed of the wave change when the wave source (car) is moving? Explain.

4. When would you hear the actual pitch of the siren of a moving ambulance? Explain.

ENRICHMENT OPPORTUNITY???? Goin’ wayyyy back…

1. Find the element with 50 protons. a. What is it? b. How many electrons does it have? c. How many neutrons does it have? 2. What group is Br in? (#) a. What is the specific name for this group? b. What are two element(s) most similar in

properties to Br? c. How many valence electrons does Br have? d. Are the elements in this group very reactive?

How do you know? 3. What is the difference between ionic and covalent

bonding? a. Explain in detail; also provide an example of each.

1. Chapter Review:

pg. 316 #3, 7-12, 15-16, 18, 21- 22, 28-29

pg. 318 #2, 3, 6, 9

2. Go over wave behavior WS

3. Check Bellringer Quiz

4. Jeopardy!

Earthquake waves model both types of waves: transverse and compressional

A. Transverse

B. Compressional

C. Longitudinal

D. Both Transverse and Compressional

A. Sound

B. Light

C. Seismic

D. Mechanical

E. Sonic Boom

A. True

B. False

A. compression

B. crest

C. trough

D. rarefaction