1. electromagnetic radiation
Overview

2. What’s Radiation? Radiation exists in many forms
Radiation- how atoms and molecules emit energy
Electromagnetic energy
nuclear energy

3. What’s Electromagnetic Radiation?
Electromagnetic (EM) Radiation- wavelike energy carried by electric and magnetic fields
generated inside matter when electrons change positions in atoms or when atoms change positions in molecules.
generated when changes occur in the nucleus of an atom

4. What’s Nuclear Radiation?
nuclear radiation- radiation produced when the nucleus of an atom changes
the nucleus changes because something makes it unstable. when that happens the nucleus gets rid of excess energy by giving off particles of EM radiation
nuclear radiation includes:
alpha particles
beta particles
gamma rays
Nuclear radiation is used in hospitals to trace blood flow and kill cancer cells

5. Why is Understanding Radiation Important?
Knowing about electromagnetic and nuclear radiation makes us better informed about the world around us
Radiation – both electromagnetic and nuclear – is involved in many technical systems
if improperly handled, either type of radiation can be life-threatening

6. How is electromagnetic radiation used?
Many industries generate, send and receive electromagnetic radiation.
Communication industries
radiowaves
TV signals
microwaves
Law Enforcement
Radar
Hospitals
X-Rays
gamma rays

7. What’s the electromagnetic spectrum?
Electromagnetic Spectrum- the total range of wavelengths or frequencies of electromagnetic radiation

8. How is EM Radiation characterized?
When describing EM radiation we usually mention three or four characteristics:
Wavelength – the distance between any point on the electromagnetic and the same point on the next wave
measured in meters
Frequency – the number of wavelengths per second
measured in hertz
Speed – how fast the EM waves travel
wavespeed = frequency x wavelength
in a vacuum or air, EM radiation moves at 3 x 108 m/s (186,000 miles/second)
Energy – the kinetic energy carried by the electromagnetic energy or wave
measured in joules

9. Example: Wavelength of a 1000-kHz radiowave
A 1000-kilohertz radio wave travels from a radio tower to a radio receiver at a speed of 3 x 108 m/s. Find the wavelength of the radiowave.
λ= 𝑣 𝑓
Given:
f = 1000 kHz
= 1,000,000 Hz
v = 300,000,000 m/s
λ = ?
λ= 300,000,000 1,000,000
λ =300𝑚

10. Example: Speed of Red Light Through Glass
Red light from a laser passes through a thick pane of window glass. The red light has a wavelength of 600 nanometers in air and 400 nanometers in glass. It has the same frequency (5× 𝐻𝑧) in both glass and air. Find the wavespeed in both glass and air.
𝑣 𝑎𝑖𝑟 =λ𝑓
𝑣 𝑔𝑙𝑎𝑠𝑠 =λ𝑓
𝑣 𝑎𝑖𝑟 =(600× 10 −9 )(5× )
𝑣 𝑔𝑙𝑎𝑠𝑠 =(400× 10 −9 )(5× )
𝑣 𝑎𝑖𝑟 =3× 10 8 𝑚/𝑠
𝑣 𝑔𝑙𝑎𝑠𝑠 =2× 10 8 𝑚/𝑠

11. How are photons and EM energy related?
Sometimes EM radiation is best described by continuous waves
When radiation travels from one point to another or when it is reflected from a surface
Other times, it’s more useful to thing of EM radiation as small packets or bundles of energy
When light interacts with matter and is absorbed
photon- a massless “packet” or “bundle” of electromagnetic radiation that carries energy and momentum
E = energy in joules
h = planck’s constant (6.63 x 10-34J-sec)
λ = wavelength in meters
c = speed of EM radiation
f = wave frequency in Hz
𝐸= ℎ𝑐 λ
or,
𝐸=ℎ𝑓

12. Example: Energy carried by Gamma-Ray Photons
Short-wavelength gamma rays are among the most energetic types of EM radiation. Consider a gamma-ray photon of wavelength λ = 1 x meters, traveling in air. Find the energy of the gamma-ray photon, in joules.
𝐸= ℎ𝑐 λ
= (6.63× 10 −34 )(3× 10 8 ) (1× 10 −12 )
=1.989× 10 −13 𝐽

13. Example: Energy carried by microwave photons
A potato is cooked on a paper napkin in a microwave oven. The microwaves have a wavelength of about 3 centimeters. Find the frequency of the microwaves and the energy of each microwave photon that’s absorbed by the photon.
𝑓= 𝑣 λ
𝐸=ℎ𝑓
𝑓= 3×
𝐸=(6.63× 10 −34 )(1× )
𝑓=1× 𝐻𝑧
𝐸=6.63× 10 −24 𝐽

14. What’s visible light?
visible light is a very small part of the electromagnetic spectrum
visible light waves range in wavelength from about 4 x 10-7 meters (violet light) to about 7 x 10-7 meters (red light)

15. What’s infrared radiation?
Infrared radiation is EM radiation just beyond the red part of the visible spectrum
longer wavelength and lower frequency than visible light
less energy per photon than red-light photons
Heat energy is carried by infrared rays
night vision scopes
sunlight

16. What’s ultraviolet radiation?
Higher frequency and shorter wavelength than visible light
sometimes called “blacklight”
Causes sunburn

17. What are microwaves?
Microwave radiation has longer wavelengths and lower frequencies than visible or infrared light
Less energy per photon than visible or infrared light sources
Microwave ovens cook food because the microwave photons have just the right wavelength to cause water molecules to vibrate faster and faster.
vibrating molecules cause heat

18. What about X-Rays?
X-Rays are used in hospitals and to check for flaws in welds
have enough energy to pass through human cell tissue but not through bones
short wavelengths and high frequencies
more energy per photon than visible light

19. Can light push a sailboat?
Plans are being made for a ship powered by a “solar sail”
this is a large, very lightweight “sail” made of something like Saran wrap
Light photons from the sun hit the sail and “bounce” off. As they do so they exert a force called “radiation pressure”
the push from each photon is very small
billions of photons hit the sail at the same time
the total effect causes a large enough force to move the sail around in space