1. The EM Spectrum
Learning Objectives: 1. Recall that electromagnetic waves form a continuous spectrum. 2. List the electromagnetic waves in order by increasing energy. 3. Describe how EM waves are used in technology.

2. Comparing Light and Sound
Electromagnetic wave
Transverse wave
Does NOT need a medium
Can travel in a vacuum
Speed = 3.0 x 108 m/s
(in vacuum)
Sound
Mechanical Wave
Longitudinal
Needs a medium
Can NOT travel in vacuum
Speed = 3.0 x 102 m/s
(in air)

3. Electromagnetic Spectrum
Visible light is only one form of electromagnetic (EM) radiation.
All electromagnetic waves are transverse.
All EM waves travel the same speed through a vacuum.
BUT the frequency, wavelength, and energy are all different.

4. Are electromagnetic waves dangerous?
The shorter the wavelength (and higher the frequency) of electromagnetic waves, the more energy that they carry.
radio waves
visible light
gamma rays
microwaves
infrared UV
X-rays
10 m
10 cm
1 mm
0.01 mm
100 nm
1 nm
0.01 nm
This content is higher tier for OCR Gateway Science.
energy increases
hazard increases
High-frequency electromagnetic waves, such as gamma rays, are potentially more harmful because they have more energy.

5. The electromagnetic spectrum
Teacher notes
This sequence, summarizing the electromagnetic spectrum and the uses of the different types of electromagnetic waves, could be used as an introduction to the electromagnetic spectrum or as a plenary or revision exercise on the electromagnetic spectrum.

6. Uses and Dangers of EM Waves
Put the waves in order from lowest to highest energy.
Infrared
Radio
Visible
Microwave

7. Uses Radio Used for television and radio programs Longest wavelength
Most diffraction, so can travel around mountains.
Dangers: Very low energy, so low danger.

8. Uses
Microwave
Lower frequencies are used for satellite television and mobile phones
Higher frequencies are used in microwave ovens (causes water molecules to vibrate and heat up)
Dangers: Higher frequencies could cause water inside cells to heat.

9. Uses
Infrared
Infrared energy is heat energy (can be used for heating and cooking).
Some frequencies are also used in remote controls.
Dangers: Infrared energy is heat so can cause burns.

10. Uses Visible Light Used to see. Used in photography.
Dangers: high intensity light can cause damage to the retinas.