Transcript Slide 1
How fast is that?
299 792 458 m / s or 3.00*108 m/s
Around the Earth 8 times in one second
1.5 seconds to the Moon
4 minutes to Mars
8 minutes to the Sun
30 minutes to Jupiter
4.24 years to the NEAREST star
Light Year
One light-year (ly) is the distance that
light travels in a year
9.46 × 1015 meters
About 6 trillion miles
Yes, that’s FAST!
Solar System Travel
Time to
Speed
Time to Jupiter
α Cen
Freeway Speed
75 mph
600 yrs
38 million yrs
Jetliner Speed
500 mph
90 yrs
6 million yrs
Concorde Speed
(Mach 2)
1350 mph
33 yrs
2 million yrs
Spacecraft Speed
(Voyager)
40,000 mph
1.5 yrs
70,000* yrs
Way Big
Our Milky Way Galaxy is only
100 000 light years across or about
600 000 000 000 000 000 miles or
6 x 1017 miles or
9.5 x 1017 km or
9.5 x 1020 meters or
950 000 000 000 000 000 000 meters
What is light?
Light is an electromagnetic wave
Oscillating electric and magnetic fields
Oscillations are in phase
In phase--When Electric field is increasing, Magnetic field is
increasing.
When E field is decreasing, Magnetic field is decreasing
More on EM wave
Electric and magnetic fields are perpendicular
to each other and the direction of travel
Transverse wave
You might have heard…
…that light acts as both particle and
wave
It does, but for most of this class, light
is a wave.
White Light
White light is made of a range of
frequencies or colors
Can be separated into six elementary
colors of the visible spectrum
Spectrum—The distribution of wavelengths
and frequencies
Visible light
Visible Spectrum—Red, Orange, Yellow,
Green, Blue, and Violet.
Indigo was demoted :<(
Roy G. Bv
EM Spectrum
Speed of EM waves
All EM waves travel at 3.00*108 m/s
Energy of EM waves depends on frequency.
Gamma rays=HIGH energy, radio waves=low
energy
Speed of the wave depends only on the
medium - constant in a constant medium
Water 75% Glass 67% Diamond 41%
Nothing can travel faster than light in a
vacuum
Measuring speed of light
Galileo was one of the first to try
Tried to determine time it took light to
travel 1.5 km. Would he be able to
measure the speed?
Now, error is less than .0001%
Wave Speed Equation:
c=fλ
Speed of light=frequency x wavelength
Example
Red light has a wavelength of 750nm.
What is the frequency? c=3.00*108 m/s
First, 750nm = 750*10-9 m =
7.5*10-7 m
Plug into c=fλ
(3.00*108 m/s) / (7.5*10-7 m) = f
f=4.0*1014 Hz