The Electromagnetic Spectrum & Properties of Waves

Sections 10.4 and 10.5

Electromagnetic Spectrum

The electromagnetic Spectrum• The electromagnetic spectrum is the entire range of electromagnetic waves, from radio waves through visible light to gamma rays

Electromagnetic Spectrum

• long wavelengths correspond to low frequencies and low energy

• short wavelengths correspond to high frequencies and high energy

• the higher frequency parts are more dangerous than the lower frequency parts

Radio Waves• Radio waves have the longest wavelength and lowest energy and

frequency compared to all other types of electromagnetic radiation.

• MRI technology uses radio waves to see inside our body.

MRI scan of the brain

Microwaves• Microwaves have the shortest wavelength and

highest frequency of all the radio waves.• Microwaves are used in: cooking food, and

telecommunications.

• Radar uses short wavelength microwaves.• Radar is used in: tracking the motion of

objects, weather forecasting, and taking images of the Earth’s surface.

A radar image of the Earth’s surface

Infrared Waves• Electromagnetic radiation that has a

wavelength longer than red light but shorter than that of radio waves.

• Infrared radiation is also referred to as heat.• Infrared waves are used in: remote controls,

infrared cameras, and CD-ROM readers.

Infrared cameras record differences in temperature.

Ultraviolet Waves• Ultraviolet waves (UV) are just beyond the visible

region of the spectrum.• This radiation possesses much more energy than

visible light.• UV waves striking your skin allows your body to

make Vitamin D.• Overexposure to UV can cause sunburns and possible

skin cancer.

Wavelengths shorter than visible light have more energy than visible light.

Wearing sunglasses and sunscreen help protect you against harmful UV radiation.

X rays• X rays have a much shorter wavelength and higher

energy and frequency than ultraviolet waves.• X rays are commonly used to photograph teeth and

bones.• X rays are also used to detect small cracks in metals

and also to photograph the inside of machines.

Gamma Rays• Gamma rays are the shortest wavelength

and highest energy and frequency of the electromagnetic spectrum.

• Gamma rays result from nuclear reactions.• Gamma rays can be used in radiation

therapy to kill cancer cells.

Gamma rays can be used to kill cancer cells.

The Visible Spectrum• The visible spectrum is the only part of the electromagnetic

spectrum that can be detected with the human eye• The band of colours visible in the rainbow (ROY G BIV)

The Visible Spectrum

• Isaac Newton discovered that white light is made up of the colours by passing a sunbeam through a triangular glass prism

• He then recombined these coloured beams into white light again by passing them through more prisms

• This shows that colour is a property of visible light

The Visible SpectrumWhy do objects appear different colours?

• We see an object as a certain colour because the object is reflecting that part of the visible spectrum

• We see something as blue or red because it reflects the blue part of the visible spectrum• We see something as white because it reflects all parts of the spectrum• We see something as black because it doesn’t reflect any parts of the spectrum

Properties of WavesWhat is a wave?• A wave is movement that transfers energy though matter or space• Light is an electromagnetic wave, transferring energy through space

Features of a Wave1. Crest: the highest point on a wave2. Trough: the lowest point on a wave3. Wavelength: the distance between two consecutive crests or troughs4. Amplitude: the maximum distance either above or below the resting

position (should be the same), which indicates the amount of energy transferred (the greater the amplitude, the brighter the resulting light, more energy)

FrequencyWhat is Frequency?• Frequency is the number of wavelengths (cycles) in a period of time• Frequency is normally given in hertz (Hz), which are cycles per second

1000 Hz = 1 kHz

1 000 000 Hz = 1 MHz

1 000 000 000 Hz = 1 GHz

Frequency

Electromagnetic Spectrum

• long wavelengths correspond to low frequencies and low energy

• short wavelengths correspond to high frequencies and high energy

• the higher frequency parts are more dangerous than the lower frequency parts