Image by sharonjoy17 from Pixabay

In scientific terms, electromagnetic radiation, or EMR, is radiant energy travelling outwards from a source in the form of a wave.  Unlike the mechanical waves studied in your previous physics courses, EMR does not require a material medium in which to move.  The EMR wave is classified by its  wavelength  (length) or by its  frequency  (oscillations per second).  For example, when you turn on a light, microwave popcorn, use a cordless remote control, talk on a cellphone, or tune into a radio station, you are using devices that operate with different types of electromagnetic radiation based on their wavelengths and frequencies.  Organizing all of the different types of electromagnetic radiation by frequency or wavelength produces an  electromagnetic spectrum.

wavelength:  the distance between adjacent points on a wave that vibrate in phase with one another (m)

 

frequency:  the number of cycles per unit of time (Hz = 1 cycle/second)

 

electromagnetic spectrum:  a general classification of all electromagnetic radiation based on wavelength, frequency, and energy

 

The rainbow in the photograph above is a natural example of a spectrum. The rainbow shows that white light can be separated into a "spectrum" of colours organized by wavelength.  The violet light has a wavelength of 400-450 nm (nm is nanometer, ×10 -9  m).  As you progress toward the red end of the rainbow, the wavelengths get longer.  Red light has a wavelength of 630-700 nm.  A rainbow is the natural expression of the visible light spectrum.  What is just beyond either end of the visible spectrum? 

 

Most EMR waves that cannot be sensed by the human eye.  Some, however, can be sensed with our skin.  Infrared waves, for example, are felt as heat; they have a wavelength slightly longer than red light, making them "invisible" (outside the visible spectrum).  The term  red hot  may have more meaning for you now.  Ultraviolet waves cause sunburns; they have a wavelength shorter than violet light, so they are also "invisible" (outside the visible spectrum).  Even though you can't most EMR waves, they can still affect you.

Although some radiations are marked as N for no in the diagram, some waves do in fact penetrate the atmosphere, although extremely minimally compared to the other radiations.

Adapted from image courtesy of NASA

 


Read
Read pages 637-640 in your textbook to find out more about the types of EMR and the electromagnetic spectrum .


Self-Check

Answer the following self-check questions then click the "Check your work" bar to assess your responses.

 

SC 1.  

Using "Table 13.1" on page 638 of your textbook, identify what is unique about visible light compared to the rest of the EMR spectrum.

 

SC 2.  

Open the Electromagnetic spectrum   Drag the green triangle to different parts of the spectrum.  Observe the energy of the wave for various parts of the spectrum then describe the relationship between the following two characteristics:

  1. frequency and energy

  2. wavelength and energy

SC 3.

An infrared wave of EMR has a frequency of 2.0×10 12 Hz. What is the wavelength of the wave?

 

   Self-Check Answer

Contact your teacher if your answers vary significantly from the answers provided here.

 

SC 1.  

The visible light part of the spectrum is unique because that is the only part of the electromagnetic spectrum that can be sensed by the human eye.

 

SC 2.

  1. The frequency and the energy of EMR are proportional; as the frequency doubles, the energy doubles.

  2. The wavelength and the energy of the EMR are inversely proportional. As the wavelength doubles, the energy halves; and as the wavelength decreases to one-third of its value, the energy triples.

SC 3.  

 

Given

 

Required

the wavelength of the wave

 

Analysis and Solution

 

Paraphrase

The wavelength of the infrared wave is 1.5 × 10 -4  m.