Electromagnetic Waves
About Electromagnetic Waves
Electromagnetic Waves – waves that carry energy without
requiring a medium
- produced by changing electrical and magnetic
fields
- behave as transverse waves
- the electrical and magnetic fields move
perpendicular to the direction of energy
travel
Because they require NO MEDIUM, electromagnetic waves
can pass through space
The energy carried by electromagnetic waves is called
electromagnetic radiation
About Electric and Magnetic Fields
Electric and Magnetic fields are areas in space where there
either an electric or magnetic force
Whenever you have a changing magnetic field you will have a
changing electric field and vice versa
- when one field changes, so does the other
The Speed of Electromagnetic
Waves
The speed of all electromagnetic waves in a vacuum (outer
space) is equal to the speed of light
Speed of Light = 300,000,000 m/s
When entering our atmosphere, or changing mediums,
electromagnetic waves slow down
- even when slowing down, electromagnetic waves
travel a million times faster than the speed of sound.
We can calculate the wavelength and frequency of all
electromagnetic waves using the same equations as before
- Because we are working with very large and very
small numbers we need to understand scientific notation
Scientific Notation
Scientific notation is a shorthand used in science and math to
write really large numbers in a shorter form using
exponents.
How It Works:
1. Place a decimal point after the first non-zero number in the
large number
2. Write out all the digits in between the first and last nonzero numbers in the large number
3. Multiply by 10e, where e is the number of times you need
to move the decimal to write the whole number
-- if e is positive, you move the decimal to the right
-- if e is negative, you move the decimal to the left
Practice With Scientific Notation
Write the following whole numbers in Scientific Notation
a) 456,000  4.56 x 105
b) .007204000  7.204 x 10-3
c) .00000001  1.0 x 10-8
Write the following as whole numbers:
a) 5.15 x 108  515000000
b) 3.662 x 10 -4  .0003662
c) 3.00 x 102  300
Multiplying and Dividing In
Scientific Notation
Multiplying and dividing in scientific notation is very easy!
Just split the equation into two parts: the decimal and the 10
to the exponent.
For Division
Divide the top decimal by the bottom decimal
Subtract the bottom exponent from the top exponent
For Multiplication
Multiply the decimals together
Add the exponents together
Practice Multiplying and Dividing
Using Scientific Notation
1. (3.33 x 107)
(1.11 x 105)
3.00 x 102
2. (5.29 x 10-9) x (8.00 x 104)
4.232 x 10-4
Using Scientific Notation to
Calculate Wavelength and Frequency
Remember that the speed of electromagnetic waves is pretty
much equal to the speed of light.
We use the letter c to represent the speed of light.
Therefore, our three wave equations are now:
c=λxf
λ=c/f
f=c/λ
Practice Problems
Practice Problem 1:
What is the wavelength of an electromagnetic wave with a
frequency of 6.00 x 1016 Hz?
Practice Problem 2:
What is the frequency of an electromagnetic wave with a
wavelength of 333 nm? (1 nm = 1 x 10-9 m)
The Electromagnetic Spectrum
Although all electromagnetic waves have the same speed,
they have different wavelengths and frequencies.
Electromagnetic waves with the longest wavelengths have the
smallest frequencies.
Electromagnetic waves with the largest frequencies have the
shortest wavelengths.
We classify electromagnetic waves on a spectrum, from
longest wavelength (smallest frequency) to shortest
wavelength (highest frequency)
Electromagnetic Spectrum Diagram
Increasing Wavelength
Increasing Frequency
List of Electromagnetic Waves
Most Energetic
Highest Frequency
Gamma Rays
Shortest Wavelength
X-Rays
Ultraviolet Rays
Visible Light
Infrared Rays
Microwaves
Lowest Frequency
Least Energetic
Radio waves
Longest Wavelength
Uses of Electromagnetic Waves
Radio Waves
-- longest wavelength, lowest frequency
-- used to transmit radio signals
Microwaves
-- actually a type of high-frequency radio wave
-- still has a very low frequency, long wavelength
-- used in radar
-- used in ovens
-- when water molecules in food absorb the
energy from microwaves, they heat up, cooking food
Uses of EM Waves (Cont’d)
Infrared Rays
-- just below “red” in the visible spectrum
-- often felt as heat
Visible Light
-- less than 1% of the EM spectrum is visible light
-- range from longest wavelengths (red) to shortest
wavelengths (violet)
-- this is what we see!
Uses of EM Waves (Cont’d)
Ultraviolet Rays
-- means beyond violet
-- small doses are used to produce Vitamin D
-- comes from the sun
-- large doses can kill and damage cells
-- often used to sterilize equipment in hospitals
X-Rays
-- can pass through soft tissue
-- used to see pictures of bones inside body
Uses of EM Waves (Cont’d)
Gamma Rays
-- highest-energy electromagnetic wave
-- can penetrate most tissues
-- creating the Incredible Hulk
-- highest frequency, shortest wavelength
-- often given out by radioactive substances
-- sometimes used in medicine, but because they are
so damaging, need to be seriously controlled