Electromagnetic Electromagnetic SpectrumSpectrum

InstructionsInstructions

• Duration of Lesson: 60 MinDuration of Lesson: 60 Min

• Read through this powerpoint presentation and Read through this powerpoint presentation and attempt the EM wave quizattempt the EM wave quiz

• You can also find this chapter in your textbook, You can also find this chapter in your textbook, chapter : chapter :

The grades of the quiz will be taken into you CA for semester 2, and you can only do it ONCE, so please make sure you understand the content of this unit.

IntroductionIntroduction

Objectives:At the end of the lesson, you will be able to

• Describe the main components of the electromagnetic spectrum.

• State the properties of ALL EM waves.• Discuss the role of the respective EM waves

and some of their applications.

What are Electromagnetic What are Electromagnetic Waves ?Waves ?

• If you have ever tuned in to listen to a radio, spoken on a handphone, turned on a light, had an X-ray taken, felt the warmth of sun on your skin.

• You have experienced electromagnetic wave

Electromagnetic waveElectromagnetic waveProduced by Simultaneous vibration

Electric fieldMagnetic field

Electric field

Magnetic field

http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=52

Wavelength of Electromagnetic WavesWavelength of Electromagnetic Waves

Hence this is the complete EM wave spectrum (the waves below in ascending order of wavelength; descending order of frequency )

Gamma rays

x-rays Ultra-violet ray

Visible light

Infra-red ray

Microwave Radio wave

Highest fShortest λ

Lowest fLongest λ

Properties of EM Wave

1. All electromagnetic waves are transverse wave

2. They do not require any medium to travel through (recall: Radiation Infra red is an EM Wave)

3. They travel at the speed of 3x108 ms-1 in vacuum (recall: speed of light light is also an EM Wave)

4. They can all be reflected or refracted

5. They can all be emitted or absorbed by matter

6. They all obey the wave equation

Where v = speed of wave (m/s)

f = frequency of wave (Hz)

λ = wavelength (m)

v =f x λ

7. Their frequencies do not change as they pass from one medium to another. However, both their speed and wavelength will change.

v =f x λ

9. They are all of neutral charge as all of them oscillate with electric and magnetic field perpendicular to each other.

8. They carry energy frm one place to another

WavesWaves

Longitudinal Waves Transverse Waves

Electromagnetic WavesElectromagnetic Waves

Properties

Electromagnetic SpectrumElectromagnetic Spectrum

Radiowave

Microwave

Infra-Red

Light

Ultra-Violet

X-ray

Gamma ray

Applications

Sound waves

Classified into

Comprises of

Overview of EM waves

Gamma raysGamma rays

Gamma rays have the shortest wavelengths and highest frequencies in the EM spectrum.

It is generated by :

Changes in energy levels in the nucleus

Some radioactive substances and certain nuclear reactions produce gamma rays.

Because of their great penetrating ability, gamma rays can cause serious illness. However when used in controlled conditions, gamma rays is useful in cancer treatment.

X-raysX-rays

X rays is generated by : a) Rapid deleceration of fast moving

electrons b) Changes in energy of innermost orbital

electrons

X-rays are used for :• diagnostic tool in dentistry and medicine.

Doctors and dentists can examine the condition of a person’s bones, the root of this teeth or the state of other inner part of the body.

• Custom officers at airports inspect the content of your luggage using X-rays.

• Industry wise, it is used to find cracks in structures just like cracks in bones.

Both Gamma rays and X- rays can be detected by:

a) photographic plates

b) ionization chamber

c) phosphorescence

Ultra-violetUltra-violet

The main source of ultra-violet radiation is sunlight and it is this radiation which gives rise to suntan and also sunburn.

Ultra-violet radiation is used in hospitals to sterilize the surgical instruments and operating theatres as it kills bacteria and viruses.

UV can be detected by:

a) Photographic plates

b) Photoelectric cell

c) Fluorescence

Visible LightVisible Light

Visible light is the part of the EM spectrum which can be detected by the human eye.

The visible light has its own spectrum which consist of the 7 colours of light :Red Orange Yellow Green Blue Indigo Violet

An example of visible light is the colourful laser light or the light from a firework.

Some of the uses of light is in optical fibres in medicine and telecommunications.

Infra-red wavesInfra-red wavesHeat can be transferred through infrared radiation.

We often think of infra red as being the same thing as 'heat', because it makes our skin feel warm.

Most of you might have seen infra-red waves in use during the SARS period. (picture on the top right hand corner). It shows a thermo-detector which is placed outside hospitals/airport to identify the warm and cool parts of a person by analyzing infra-red radiation emitted from the person’s body. And through this we can see if someone is having a fever.

Infra red is useful for:

- For navigation through fog & haze as it is less easily scattered compared to visible light

- Medical treatment : to warm injured muscles/sports injuries

MicrowavesMicrowavesOne of their most common uses is in microwave ovens. When you switch on a microwave oven , it gives off electromagnetic waves that bounce around inside the oven, penetrating the food. Water molecules in the food absorb the energy from the microwaves, causing the food to get hot.

Other uses of microwaves: a) Radar communication (as it is not easily

blocked of by buildings/trees)b) Analysis of fine details of molecular and

atomic structurec) Useful demonstration of all wave

properties on macroscopic scaled) Telephone communication (mobile

phones, etc)

Radio wavesRadio wavesRadio waves are the electromagnetic waves

with the longest wavelengths and lowest frequencies

Like all electromagnetic waves, radio waves can travel through a vacuum. However most of the radio waves we receive have traveled through air. Take the radio as an example. The radio converts the electromagnetic waves into the sound that comes out of the radio speakers.

Uses of radio waves:a) Radio and television communication

(to transmit sound and picture information over long distance)

b) Radar & satellite communicationc) Navigation or ships & aircrafts

WavesWaves

Longitudinal Waves Transverse Waves

Electromagnetic WavesElectromagnetic Waves

Properties

Electromagnetic SpectrumElectromagnetic Spectrum

Radiowave

Microwave

Infra-Red

Light

Ultra-Violet

X-ray

Gamma ray

Applications

Sound waves

Classified into

Comprises of

Some tips to help you to remember:• EM Spectrum

Raja’s Mother Is Visiting Uncle Xavier’s Garden

• Visible Light Spectrum

Run Off You Girls Boys In View

Radio wave

Micro wave

Infra-red Rays

Visible light

Ultra-violet ray

X-rays Gamma rays

red orange yellow green blue indigo violet

Congratulations!

You’ve completed the ELECTROMAGNETIC WAVES lesson

Please take the quiz when you’re ready !

(Remember the Quiz will be closed by Friday, 7 Sept, 23.59PM)

See you soon in Physics Class!