The Electromagnetic Spectrum
Overview
Hold your hand in front of a television remote control and press a button. Nothing happens. Point the remote at the television across a dark room and the channel changes instantly, with no wire, no sound and nothing at all for your eyes to see. Something crossed that room, carried energy from the little diode in the remote to the sensor on the television, and did it at three hundred million metres every second. It was the same kind of thing that lets you see this page, the same kind of thing that cooks a potato in a microwave oven, the same kind of thing that photographs the bone in a broken wrist. One family, one speed, one continuous spread of possibilities.
This lesson takes that family apart and puts it back in order. You will learn the sequence of the seven regions and what actually changes as you walk along it, why the strip your eyes can detect is such a thin slice of the whole and why different wavelengths inside it look like different colours, which regions carry our phone calls and our television and why each of them was chosen, what every region is used for beyond communication, and where along the sequence radiation stops merely warming you and starts tearing electrons off your molecules. By the end you should be able to take a wavelength you have never met before, put it in its place on the line, and say what it is used for and what it would do to you.
Objectives
- Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same speed through a vacuum (space). Students should know the order of electromagnetic waves within the spectrum, grouped in terms of energy, frequency and wavelength. They should appreciate that the wavelengths of the electromagnetic spectrum range from 10-15 m to 104 m and beyond.
- Visible light is the part of the electromagnetic spectrum that is detected by our eyes; we see different wavelengths as different colours.
- Radio waves, microwaves, infrared and visible light can be used for communication.
- Electromagnetic waves have many practical applications. For example: radio waves - television and radio systems (including Bluetooth); microwaves - mobile phones and satellite television systems; infrared - TV remote controls, night vision devices, heating; visible light - photography, fibre optic communications; ultraviolet - security marking 22 ; X-rays - medical imaging; gamma rays - sterilising surgical instruments and killing harmful bacteria in food.
- Excessive exposure of the human body to electromagnetic waves can be hazardous. Low energy waves have a heating effect and higher energy waves have enough energy to cause ionisation (remove an electron from an atom or molecule). For example: microwaves - heating of body tissue; infrared - skin burns; ultraviolet - skin cancer and blindness; X-rays - high doses kill cells; gamma rays - genetic mutations. Students should be able to describe simple protection measures against risks.
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on The Electromagnetic Spectrum. Now that you've explored the key concepts and ideas, it's time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Which list gives four types of electromagnetic wave in order of increasing frequency? A. Infrared, microwaves, ultraviolet, X-rays B. Microwaves, infrared, ultraviolet, X-rays C. X-rays, ultraviolet, infrared, microwaves D. Ultraviolet, X-rays, microwaves, infrared Answer: B
- Two electromagnetic waves travel through a vacuum, one a radio wave and one a gamma ray. Which statement is correct? A. The gamma ray travels faster than the radio wave B. The radio wave travels faster than the gamma ray C. They travel at the same speed D. Neither can travel through a vacuum Answer: C
- Which type of electromagnetic radiation is used for security marking? A. Microwaves B. Infrared C. Ultraviolet D. Gamma rays Answer: C
- Which type of electromagnetic radiation is used by a television remote control? A. Radio waves B. Microwaves C. Infrared D. Ultraviolet Answer: C
- A microwave transmitter emits waves of frequency 6.0 x 10^9 Hz. Electromagnetic waves travel at 3.0 x 10^8 m/s. What is the wavelength of the waves? A. 0.005 m B. 0.05 m C. 0.5 m D. 20 m Answer: B
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Recommended Books
Further learning from open sources
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Textbook section
The Electromagnetic Spectrum
Define the electromagnetic spectrum, and describe it in terms of frequencies and wavelengths
"Physics: The Electromagnetic Spectrum" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/physics/pages/15-1-the-electromagnetic-spectrum. Access for free at https://openstax.org/books/physics/pages/1-introduction
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Textbook section
Biological Effects of Ionizing Radiation
We hear many seemingly contradictory things about the biological effects of ionizing radiation. It can cause cancer, burns, and hair loss, yet it is used to treat and even cure cancer. How do we understand these effects? Once again, there is an underlying simplicity in nature, even in complicated bi
"College Physics: Biological Effects of Ionizing Radiation" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/32-2-biological-effects-of-ionizing-radiation. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
Published by other organisations under open licences, credited as they ask. Links open their websites.
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