EM Spectrum

What are waves classified by?

wavelengths

Which EM wave has the longest wavelength and the lowest frequency?

Radio wave

Which EM wave has the shortest wavelength and the highest frequency?

gamma radiation

Order of EM Waves with increasing wavelength

Gamma → X-ray → UV → Visible → Infrared → Microwave → Radio waves

Can regions in the EM spectrum overlap?

Regions in the electromagnetic spectrum are not clearly separated and may overlap.

Wavelength of visible light is often written in …

nanometres

The frequency of EM radiation depends on ..

body temperature

Radiation is emitted when …

atoms of the body lose energy that they had gained when the body was given heat.

Properties of EM Waves (10)

1. EM waves are transverse waves.

2. They are electric and magnetic fields that oscillate at 90 degrees to each other.

3. They transfer energy from one place to another.

4. They can travel through a vacuum. They do not require a medium to travel.

5. They travel at the speed of 3.0 x 10⁸ m s^-1 in vacuum. They will slow down when travelling through glass, etc…

6. They obey the wave equation, v = fλ.

7. They obey the laws of reflection and refraction.

8. They carry no electric charge.

9. Their frequencies do not change when they travel from one medium to another. This is because frequency f depends only on the source of the wave.

10. Their speeds and wavelengths change from one medium to another.

EM waves are … waves

transverse

EM waves are electric and magnetic fields that oscillate at … to each other

90 degrees

Do EM waves transfer energy?

Yes

Do EM waves require a medium to travel?

No

EM waves travel at a speed of … in a vacuum

3.0 x 10⁸ m s^-1

EM waves slow down when..

travelling through different mediums

EM waves obey the wave equation …

v = fλ.

EM waves follow the laws of …

reflection and refraction

EM waves carry … electric charge

no electric charge

When travelling from one medium to another, EM waves’ … do not change.

frequency

Frequency does not change when traveling from one medium to another because…

 frequency f depends only on the source of the wave

… and … change when EM waves travel from one medium to another

speed and wavelength

How are radio waves produced?

 from an alternating current in a tuned electrical circuit

What are higher frequency radio waves used for?

rapid transfer of information in satellite television/internet

Why are higher frequency radio waves used for rapid transfer of information in satellite television/internet?

because can carry more information per unit time compared to lower frequencies

What are lower frequency radio waves used for?

traditional radio stations

What are radio waves generally used for?

Radio and television communication

How are microwaves produced?

oscillations of electrons in a vacuum

What are microwaves used for?

• 2450 Hz → microwave ovens for cooking

• Transfer data for satellite television broadcasts 

• Short-range internet links

How do microwave ovens work?

microwaves of 2450 Hz are used in ovens as it allows water molecules that have a natural frequency of 2450 Hz to resonate with it. Water molecules gain kinetic energy and increase in temperature to cook food

What EM wave radiation is given out at a frequency of around 10¹³ Hz and by bodies at room temperature?

Infra-red

What are infra-red radiation used for?

• Television remote controls

• Intruder alarms

• Night vision binoculars to indicate presence of warm objects when visible light is absent

How do night-vision binoculars work?

With infrared, to indicate presence of warm objects when visible light is absent

Different frequencies of light are seen as … in the human brain

different colours

Amongst visible light, which has the lowest frequency but longest wavelength

red

Amongst visible light, which has the highest frequency but shortest wavelength

violet

What is visible light used for?

Optical fibres for medical uses and telecommunications

How is UV radiation produced?

by high energy electron transitions

Which EM wave causes emission of visible light for certain substances

Ultraviolet

Give an example of UV causing emission of visible light for certain substances.

white clothes glow under UV disco lights

What is UV used for?

• Sunbeds

• Sterilisation

When are X-rays produced?

when high energy electrons collide with a metal target

What does X-ray’s high frequency allow it to do?

allows it to pass through matter and affect photographic film

What are X-rays used for?

• Radiological /Engineering applications

• Reveal inside of object photographed with X-rays

What are gamma rays?

Energies in the order of megaelectronvolt

When are gamma rays produced?

when a nucleus loses energy after a nuclear reaction

What is gamma radiation used for?

Cancer Treatment

Which EM wave is most penetrative to fog?

Gamma radiation

What happens when your body absorbs radio waves or microwaves?

> slight heating
> do not change cell structure
> can interfere with electronic devices like pacemakers/cause malfunction

What happens when your body absorbs infrared radiation?

> cause burns
> low levels are harmless

What happens when your body absorbs visible light?

> high power like lasers can damage eyes, burn skin

What happens when your body absorbs UV?

> triggers release of chemicals in skin that cause redness and swelling that looks like a burn
> can change structure of the skin’s DNA and cause skin cancer

What happens when your body absorbs X-rays or gamma radiation?

> Ionization of living cells’ atoms affect the cell’s ability to carry out its function/rupture cell wall.
> If a large amount of cells of a vital organ become affected, the organism could die.

What is ionization?

> Ionization of atoms is when energy is used to remove electrons from atoms.

State two properties of X-rays that enable them to be used to detect broken bones.

X-rays can penetrate matter such as tissues but not dense matter such as bones. X-rays cause fluorescence on photographic plates and films.

Explain how X-rays can be used to photograph your bones.

• X-rays can penetrate matters such as tissues and bones by different amounts/degrees.

• X-rays will produce a pattern of varying depths of blackness (due to the patient's tissues) on the film.

• The X-ray film develops such that areas that were exposed to the X-rays were darker.

• Dense objects such as bone and metal fragments display brighter because they block more of the X-ray, reducing the film’s exposure.