1. Waves, Light, and the EM Spectrum
What is a wave?
What are the main properties of waves?
What two things do all waves transport?

2. Waves are a type of disturbance that can propagate or travel.
Waves carry information and energy.
Properties of a wave
wavelength ()
crest
amplitude (A)
trough
velocity (v)
Period (T): time between crest (or trough) passages
Frequency (f): rate of passage of crests (or troughs), f
wave speed = wavelength/period = wavelength * frequency 1 T
(units: Hertz or cycles/sec)
(v = f)

3. Resonance Natural frequency Resonance
Determined by elasticity and shape
Bells, violin strings, idling cars
Resonance
Dramatic increase in amplitude at natural frequency
Pumping a swing
(Tacoma Narrows Bridge Video)
(Web Link)

4. Resonance and Black Holes
If a normal object (e.g. pizza dough) rotates fast enough what happens to it?
What about a loose car tire on a fast moving car?
What is the shape of the event horizon of:
a nonrotating black hole?
a rotating black hole?

5. Resonance and Black Holes
If a normal object (e.g. pizza dough) rotates fast enough what happens to it? it will be torn apart
Will the same thing happen to the black hole?
A loose tire can borrow rotational energy and wobble at its natural frequency
Enough energy => car loses tire!
What is the shape of the event horizon of:
a nonrotating black hole? spherical
a rotating black hole? elongated (bulges at equator)
A rotating black hole can “pulsate” like loose tire
Can a black hole destroy its own event horizon?

6. Cosmic Censorship
A black hole cannot shed its event horizon by any known mechanism
Cosmic censorship theorem
There can exist no “naked” singularities
Nature requires that a singularity always be shrouded by an event horizon
We can never directly observe a singularity
Unfortunate, since offers best clue to quantum gravity

7. Electric Force - opposites attract, likes repel
Oscillating charges radiate
All objects have temperatures greater than absolute zero - random thermal motion
All ordinary objects radiate!
Why don’t we see the radiation coming from many ordinary objects?
Dog whistle analogy

8. Electromagnetic Radiation
(How we get information about the cosmos)
What are some examples of electromagnetic radiation and what are the different ways in which we might experience them or make use of them?

9. Electromagnetic Radiation
(How we get information about the cosmos)
What are some examples of electromagnetic radiation and what are the different ways in which we might experience them or make use of them?
Light (see)
Infrared (heat)
Ultraviolet (sunburn)
Microwaves (cooking, communication)
AM radio (communication)
FM radio (communication)
TV signals (communication)
Cell phone signals (communication)
X-rays (medial applications)

10. Bigger  means smaller f
The speed of all electromagnetic waves is equal to the speed of light.
c = 186,000 miles / s
or c = 300,000 km / s
light takes 8 minutes
Sun
Earth
c =
f
Bigger  means smaller f
A changing electric field creates or induces a magnetic field and vice-versa!
(Shockwave Demo) (Web Link)

11. The Electromagnetic Spectrum
1 nm = m , 1 Angstrom = m
c =
f

12. The Doppler Effect
How does the pitch or tone of a sound wave change when the source of the sound is moving towards or away from you? (Link to Demo)
What about when you are moving
towards or away from the source?
at a right angle to the source?
Does this effect occur for all types of waves or just for sound waves?

13. The frequency or wavelength of a wave depends on the relative motion of the source and the observer. (Shockwave Demo) (Web Link)
How does a change in frequency affect how we perceive visible light?

14. Frequency Shifted EM Waves
Frequency (or wavelength) of light determines color.
Red shift: longer wavelength and lower frequency
Blue shift: shorter wavelength and higher frequency
Gravity can also cause a frequency shift!
Energy of EM radiation is proportional to its frequency
What happens to EM radiation trying to escape a black hole?

15. Frequency Shifted EM Waves
Frequency (or wavelength) of light determines color.
Red shift: longer wavelength and lower frequency
Blue shift: shorter wavelength and higher frequency
Gravity can also cause a frequency shift!
Energy of EM radiation is proportional to its frequency
What happens to EM radiation trying to escape a black hole?
Radiation is infinitely red-shifted => no energy can escape!