Information in Radio Waves
Name: ______________________________ Class:________ Date:________
Conversions and Calculations Using Light Speed
Everyone knows that light travels fast. In fact, current physical laws state that nothing in
the universe should be capable of moving faster than the speed of light. But exactly how fast is
this? How do we know?
The first attempts to measure the speed of light were the same way the speed of any
other object is measured, distance traveled over time. The problem with this is that light is so
fast it travels between points on Earth seemingly instantaneously. The first real calculations of
light speed came from the shadows of Jupiter’s moons. When Earth was closest to Jupiter, the
orbit of Io seemed ahead of schedule and vice versa. More accurate measurements after that
came from rotating mirror systems. The most accurate and modern measurements come from
atomic clocks. You will be making the same measurements, but your job will be much easier as
you get to work with more known values.
Known Values and equations:
V = d / t (where V = velocity, d = distance, and t = time)
distance of Earth to Sun = 149,597,870.7 km
Time it takes light to travel from the Sun to Earth = ~ 8 minutes and 19 seconds
Calculate the following:
1.) Speed of light:
v = 149,597,870.7 km / (60 x 8 + 19) s
v = 299,795 km / s
2.) Light year:
299,795 km x 60 x 60 x 24 x 365.25
9,460,810,692,000 km
3.) Time for light to travel from Earth to mars (avg. distance of 225 million km):
299,795 km / s = 225,000,000 km / t therefore t = 225,000,000 km / 299,795 km / s
750.5 seconds
or
` 12 minutes and 30 seconds
Information in Radio Waves
Now that you have calculated the velocity of light, you are able to make more calculations based
on it. As you may know, there is more than one type of light. Each type of light has a different
range of frequency and a different range of wavelength. Because of this, the speed of light can
be broken down into a slightly different equation:
V = f * 𝜆 (where f = frequency and 𝜆= wavelength)
frequency = waves per second
wavelength = length of individual waves (duhh….)
For these problems, calculate values with the actual speed of light: 299,792,458 m / s
4.) Wavelengths of visible light: (frequencies of 430 THz to 790 THz)
390 to 700 nm
5.) Frequency of atomic hydrogen hyperfine transition:
𝜆 = 21 cm
` 1420.4 MHz
6.) Calculate the frequencies corresponding to each wavelength provided:
a - 3 m: 99.9 MHz
b - 500 nm: 600 THz
c - 30 pm: 10 EHz
7.) Calculate the wavelengths corresponding to each frequency provided:
a - 50 MHz: 600 cm
b - 30 kHz: 10 km
c - 200 GHz: 1500 𝜇m
Information in Radio Waves
Metric prefixes
Prefix
Symbol
1000
m
10
n
Decimal
US English
[n 1]
word
Since
n 2]
yotta
Y
1000
8
10
24
1000000000000000000000000
septillion
1991
zetta
Z
1000
7
10
21
1000000000000000000000
sextillion
1991
exa
E
1000
6
10
18
1000000000000000000
quintillion
1975
peta
P
1000
5
10
15
1000000000000000
quadrillion
1975
tera
T
1000
4
10
12
1000000000000
trillion
1960
giga
G
1000
3
10
9
1000000000
billion
1960
mega
M
1000
2
10
6
1000000
million
1960
kilo
k
1000
1
10
3
1000
thousand
1795
hecto
h
1000
2/3
10
2
100
hundred
1795
deca
da
1000
1/3
10
1
10
ten
1795
0
10
0
1
one
–
1000
deci
d
1000
−1/3
10
−1
0.1
tenth
1795
centi
c
1000
−2/3
10
−2
0.01
hundredth
1795
milli
m
1000
−1
10
−3
0.001
thousandth
1795
micro
µ
1000
−2
10
−6
0.000001
millionth
1960
nano
n
1000
−3
10
−9
0.000000001
billionth
1960
pico
p
1000
−4
10
−12
0.000000000001
trillionth
1960
femto
f
1000
−5
10
−15
0.000000000000001
quadrillionth
1964
atto
a
1000
−6
10
−18
0.000000000000000001
quintillionth
1964
zepto
z
1000
−7
10
−21
0.000000000000000000001
sextillionth
1991
yocto
y
1000
−8
10
−24
0.000000000000000000000001
septillionth
1991
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