PHYSICS - WAVES - Electromagnetic spectrum

Electromagnetic spectrum

All electromagnetic waves arranged by their wavelength and frequency

These waves travel at the speed of light in a vacuum (3 × 10^8)

Relationship between wavelength and frequency

They are inversely proportional

c = y x f

c = speed of light

High frequency waves have shorter wavelength and more energy

Low frequency waves have longer wavelength and less energy

Order of spectrum (lowest to highest frequency)

Radio waves, microwaves, infared radiation, visable light, ultraviolet radiaton, X-rays, gamma rays

Radio waves

wavelength 1m to 1000m

lowest frequency 3 - 3 × 10^11Hz

sources - electronic circuits

detectors - aerials

uses - communication

safe unless highly concentrated

sources of radiowaves

natural:

lighting

cosmic sources

artificial:

oscillating electric circuits

mobile phone towers, satellite communication systems

detection of radio waves

aerials

radios - receive signals and convert them into sound waves

radio telescopes

uses of radiowaves

AM FM modulation

TV broadcasting - transmit audio and video signals for TV

How radiowaves are produced

alternating current in circuit produced oscillating electric and magnetic fields

oscillations create radio waves that travel through space in all directions

antennas receive wavesand convert them into electrical signals

Microwaves

wavelength 1mm to 1cm

frequency 3 × 10^8 - 3 × 10^11

sources - electronic circuits

detectors - aerials

uses - satellite communication, microwave ovens, radar

can cause burns if concentrated

sources of microwaves

natural:

remnants of Big Bang

artificial:

microwave ovens - generate microwaves using magnetron

radar systems - detecting objects

communication devices

detection of microwaves

aerials

satellite dishes - cature microwave signals from satellites for communication broadcasting

uses of microwaves

microwave ovens - heat food by causing water molecules to vibrate, generating heat, to make cooking faster

cancer therapy - used in hyperthermia to kill cancer cells

How microwaves are produced

magnetrons - used in microwave ovens by accelarating electrons in a magnetic field

oscillators - generate microwaves for various communication systems

Infared radiation

wavelength 750 nm - 1mm

frequency 3 × 10^11 - 430 × 10^11Hz

sources - warm objects, sun, electronic devices

detectors - heat-sensitive papers infared cameras

uses - remote controls, thermal imaging, night vision, heaters

can cause burns if concentrated

Sources of infared radiation

natural:

sun

warm objects (objects above -273⁰C)

Earth and other planets emit infared due to heat absorbed from sun

artificial:

infared lamps - used for heating

electrical appliances - radiators, heaters, and toasters

infared LED - found in remote controls, and sensors

detection of infared radiation

infared cameras - capture ir and convert it into images showing temperature variations

thermometers - measure temperature by detecting infared radiation emitted by an object

uses of infared radiation

thermal imaging

heaters - provide warmth

cooking - grills, toasters, and ovens for heating food

night vision - infared goggles or cameras allow visibility in darkness by detecting heat

Visible light

wavelength 380nm - 750 nm

frequency 4 × 10^14

red 700nm, violet 400nm

sources - sun, LED, light bulbs

detectors - human eyes, cameras, LDR

uses - vision, photography

can cause blindness or burns if too intense

Sources of visible light

natural:

sun

stars

fire

artificial:

light bulbs

screens

lasers

detection of visible light

cameras

photodiodes - convert light into electrical signals

LDR - detect changes in light intensity

uses of visible light

vision

lighting - illumination of homes, streets, and workplaces

optical fibers - used in fibre-optic cables to transmit data over long distances

astronomy - telescopes use it to observe stars, planets, and galaxies

microscopy

How visible light is produced

incandescence - light is emitted by objects when heated to high temperatures

luminescence - light produced without heat, such as LED, fireflies

emission from atoms - when electrons in an atom gain energy and return to thei lower energy stats, they emit light

UV radiation

wavelength 10nm - 380nm

frequency 7.5 × 10^14

sources - sun, gas discharge lamps

detectors - fluorescent materials, photographic film

uses - sterilisation, producing vitamin D, detecting forged documents

can cause sunburn, skin cancer, eye damage

Types of UV radiation

1.UVA (315 - 400nm)

longest wavelength, lowest energy

causes tanning and skin aging

2.UVB (280 - 315nm)

medium energy

causes sunburn and skin cancer

vitamin D production

3.UVC (100 - 280nm)

shortest wavelength, highest energy

Most harmful but absorbed by Earth’s ozone layer

Sources of UV radiation

natural:

sun

high-energy cosmic phenomena

artificial:

tanning beds - emit UVA and UVB

black light - emit long-wave UVA

UV lamps - used in water sterilisation

detection of UV radiation

fluorescent materials - causes certain materials to glow

photographic film

UV sensors

medical uses of UV radiation

sterilisation and disinfection - kills bacteria, viruses, and microorganisms

vitamin D - UVB triggers synthesus if vitamin D in human skin

industrial uses of UV radiation

forensic science - used to detect body fluids, bloodstains, and fake money

black lights - creates glowing effects on fluorescent materials

X-rays

wavelength - 0.01nm - 10nm

frequency 10^16 - 19 Hz

sources - high-energy electrons hitting a metal target

detectors - photographic film, geiger muller tube

uses - medical imaging, security scanning

can damage cells, cause mutations, cancer

Sources of X-rays

natural:

high energy cosmic phenomena

artificial:

high energy electrons strike a metal target

nuclear reactions

detection of X-rays

x-ray detectors - x-rays darken photographic film, allowing creation of x-ray images

geiger muller tubes

fluorescent screens

medical uses of x-rays

medical imaging - pass thrpugh soft tissues but absorbed by bones, allowing detection of fractures, dental issues

CT scans - create 3D images of body

radiotherapy - destroy cancerous cells

industrial uses of x-rays

security scanning - inspect luggage for dangerous items

NDT

analysis of composition of materials

How x-rays are produced

high voltage accelerates electrins through vacuum tube

electrons collide with metal target causing deceleration of them

deceleration produces x-rays due to conversion of kinetic energy to electromagnetic energy

Gamma rays

wavelength < 0.01nm

highest frequency 10^19Hz

sources - radioactive decay, nuclear reactions

detectors - photographic film, geiger muller tube

uses - cancer treatment (radiotherapy), sterilisation of medical equipment

can destroy cells, cause severe mutations

wave speed of all electromagnetic waves in vacuum

3 × 10^8, speed of light

planck’s constant

h = 6.626 × 10^-34

E = hf

protection from high-frequency electromagnetic waves

sunscreen or lead aprons

Sources of gamma rays

natural:

radioactive decay

black holes and neutron stars

artificial:

nuclear reactions

nuclear power plants

medical equipment for cancer

detection of gamma rays

geiger muller tubes - detect radiation by ionisation of gas

photographic film - darkens when exposed to gamma rays

scintillation counters - measure light emitted when gr interact with certain materials

cloud chambers - visualise paths of ionising radiation

medical uses of gamma rays

cancer treatment - used to kill cancer cells without damaging too much surrounding healthy tissue

sterilising - kills bacteria, viruses, and fungi

industrial uses of

examining welds, detecting cracks or flaws in metal structures

killing bacteria and parasites in food to increase shelf life

How gamma rays are made

nuclear reactions or decay of radioactive isotopes

created during nuclear fusion, fission, and high energy cosmic phenomena

symptoms of radiation sickness

nausea, weakness, death