PHY - 2. EM spectrum

give the order of the EM spectrum

• radiowaves

• microwaves

• infrared radiation

• visible light

• ultraviolet

• x-rays

• gamma rays

properties of waves on EM spectrum

• travel at the speed of light - 3×10⁸ (all waves)

• don’t require a vacuum to travel e.g. can travel in space

fun fact about space

there is no sound in space as they require a medium (sound particles)

uses and dangers of radio waves

• communication

• navigation

• air traffic control

• can slightly raise temp.

• negligible

• reduce exposure time

• metal shielding

uses and dangers of microwaves

• communication

• cooking food

• weather radars

• heating human tissue internally

• can cause burns in high dosage

• reduce exposure time

• metal shielding

uses and dangers of infrared

• electrical heating

• remote controls

• thermal imaging

• damages eyes

• can cause burns

• protective clothing/ goggles

uses and dangers of visible light

• sight/vision

• communication

• medicinal

• agricultural monitoring

• eye damage

• skin damage

• sleep disruption

• sunscreen, sunglasses, hats

• reduce exposure to direct sunlight

uses and dangers of ultraviolet

• kills bacteria

• creates fluorescence

• tanning beds

• checking for counterfeit money

• eye damage

• skin damage

• skin cancer

• sunscreen, sunglasses, hats

• reduce exposure to direct sunlight

uses and dangers of x-ray

• x-rays of bones, teeth etc (medicinal)

• observing the internal structure of objects and materials (security)

• telescope

• small risk of cancer

• ionization can cause cellular damage/ mutation

• lead shields/ aprons

• minimizing exposure time

• maintaining distance

uses and dangers of gamma rays

• cancer treatment

• sterilisation and disinfection

• can cause cancer/ damage cells - are highly ionising and have lots of energy

• radiation poisoning/burns

• lead shields/ aprons

• minimizing exposure time

• maintaining distance

why do bones show up white on x-rays

• x-ray waves can’t pass through the bones (too dense) and therefore absorb the x-rays

• this makes the bone the negative space as the x-rays can pass through tissue

• in order to make it easier to see they flipped it so negative space = white and positive = black

why are gamma rays useful to us

• they have a high frequency and high ionisation due to their high energy

• this can be used to treat cancer by damaging the cancerous cells

how do gamma rays cause damage

The rays can damage DNA when they pass through it and when this happens it creates a risk of cancer due to ionising ability of gamma

why is food sometimes irradiated using gamma rays

They have enough radiation to sterilise materials

In food this will kill bacteria

and it extends the shelf life of the food

explain ow 2 different EM radiations make checking counterfeit bank notes possible

• UV and Visible light

• UV is absorbed by the banknote

• visible light is emitted from the banknote