Electromagnetic Spectrum

State the EM waves in order of wavelength from longest to shortest.

Radio, micro, infrared, visible, UV, X-ray, gamma

What are the common features of all EM waves? (5)

• all can travel through a vacuum

• all are transverse waves

• all travel at the speed of a light in a vacuum

• all are vibrations of electric and magnetic fields

• all radiate / spread out from their source

What are the common differences of EM waves? (4)

• They all have different wavelengths

• they all have different frequencies

• some waves like UV, X-rays and gamma rays cause cancer, but others don’t

• the only EM wave our eyes can detect is visible light

How is each EM wave produced?

• radio waves - oscillations in electrical circuits.

• microwaves - electronic devices like magnetrons in microwave ovens and some electric circuits

• infrared - vibration of molecular bonds (heat).

• visible light - electrons within atoms change energy levels / shells

• UV - also when electrons within atoms change energy levels, but with higher energy transitions

• X-rays - high-speed electrons rapidly decelerating in X-ray tubes

• Gamma rays - changes in the nucleus of an atom. produced in radioactive decay when unstable nucleus emits excess energy

How is each EM wave detected?

• Radio waves - by aerials / antennas. creates AC in an electrical circuit.

• Microwaves - antenna / metal grid detector. converted into electrical signals.

• Infrared - thermal imaging cameras, photodiodes, etc. Generates an electrical charge converted into a thermal image.

• Visible light - human eye, photographic film. Light converted into electrical signals.

• UV - fluorescent materials / photodiodes. fluorescent materials glow under UV.

• X-rays - photographic film. Creates electrical signals like in X-rays of human bodies.

• Gamma rays - Geiger-Muller tubes or scintillation crystals. Gamma ionises gas in GM tube, causing a click which is counted.

What are 1-2 uses of each EM wave?

• Radio waves - TV broadcasting, satellite communications

• Microwaves - Satellite communications, cooking food

• Infrared - electrical heaters, optical fibres

• Visible light - photography

• UV - energy-efficient lamps

• X-rays - medical imaging, airport security

• Gamma rays - sterilising food, treating cancer

How is each EM wave dangerous?

• Radio waves - no harm to human health (carry very little energy)

• Microwaves - skin burns

• Infrared - skin burns, tissue damage

• Visible light - blindness, damage to eyes

• UV - sunburn, premature ageing, skin cancer

• X-rays - DNA mutations, leading to cancer

• Gamma rays - Tissue damage, cell mutation leading to cancer

How can each EM wave’s impact be mitigated?

• Radio waves - no precautions required

• Microwaves - use metal shielding like mesh on microwave doors

• Infrared - limited intensity and duration of exposure

• Visible light - avoiding staring directly at very bright light sources

• UV - suncreams

• X-rays - stand behind lead-lined screens / leave the room

• Gamma rays - handle radioactive substances with long tongs

formula for wavespeed?

v (m/s) = f (Hz) x lambda (m)

Speed of light in a vacuum?

300 million m/s

How much is 1KHz and 1MHz?

1 KHz = 1000Hz, 1MHz = 1 million Hz

define frequency

total number of complete wave cycles in one second

formula for time period?

T (s) = 1/f (Hz)