Science 30 - Electromagnetic Energy (Unit C)
Lesson 28 – Electromagnetic Radiation
Electromagnetic radiation or EMR – a wave that consists of changing electric field and a changing
magnetic field travelling at right angles (transverse) to one another. The radiation doesn’t need a
medium to move through (like air or water) and can move through a vacuum.
Radiation can be in the form that we can feel in thermal radiation (heat), that we can see (light), we
can transmit (radio waves), and those we can’t see X-Ray/UV/gamma rays. These are all put
together on the electromagnetic spectrum (found in your data booklet)
Video – EMR
Calculating Wavelength and Frequency
Wavelength – The length of one complete vibration of the wave or cycle (i.e. from crestcrest). The symbol for wavelength is the Greek letter lambda
Practice Problems: Calculate the wavelength for each of the following waves.
Example #1
Example #2
Frequency – The number of cycles per second (measured in Hz). For example, 5 cycles per second looks
like f=5 Hz. Put the time in seconds first to make things easier, when calculating frequency.
Example Problem #3 If the following passes a detector in 0.3 seconds, what is the frequency?
Example Problem #4
In 1.00ns, 840 radio waves pass the antenna of a radio.
Universal Wave Equation - The universal wave equation is said to be universal because it applies to all
types of waves.
v=f
There is a very wide range of wavelength and frequency values, but the speed of all these waves
travelling through a vacuum or air is the same, 3.00 X 108m/s (the speed of light).
The speed of light is given its own symbol, c. In your data book:
v = c = 3.00 X 108 m/s [for all EMR]
Combine this with the regular v = d/t formula and you can find the distance a wave travelled over a
certain time.
Example Problem #5
An excited atom in a neon sign emits EMR with a wavelength of 6.4 X 10-7m.
a) Calculate the frequency
b) If the sign was 25.0m away, how long did it take the wave to reach the observer.
Homework:
p. 417-421 #5, 6-8
p. 434 #2-3
Complete the EMR Table Worksheet