Topic 4: Electromagnetic Radiation (EMR)

What does frequency or wavelength mean? What does ionizing mean?

Why is it important to study Electromagnetic Radiation?

What do you notice from this table?

Origin of EMRWhat exactly is electromagnetic radiation? • EMR is a wave that consists of a changing electric field and

a changing magnetic field that travels at right angles to one another

• When an electron moves between 2 points back and forth, this creates a changing electric field, therefore changing magnetic field and EMR

Make sure you color code your picture!

Watch this video for a quick introduction to EMR

EMR Terminology• Cycle – one completed vibration of a

wave (one crest and one trough)

• Wavelength – length of one cycle– Example: One maximum and one

minimum– Wavelength is measured in meters

and represented by the symbol λ

• Frequency - # of cycles/second– Frequency is measured in Hz (Hertz)

and represented by the symbol f

Label the following as low frequency/long wavelength and high frequency/short wavelength.

High frequency and short wavelengths

Low frequency and long wavelengths

Electromagnetic Spectrum• All portions of the spectrum, visible light, infrared, radio

waves and ultraviolet are fundamentally the same. • They are waves of alternating electric and magnetic fields that

all move through space at the "speed of light" (called “C”) of 3.00 x 108 m/s

• That’s eight times around the Earth in the tick of a clock.

This is on page 3 of the data booklet!!!

How are radio waves different from X-rays?

•Different types of radiation simply have different source, wavelengths and frequencies

• For example visual light is in the middle of the spectrum, with wavelengths that extend from 400 nm for violet light to about 700 nm for red light

Electromagnetic Spectrum

• Because EMR have different frequencies and wavelengths, this means they carry different amounts of energy (photons)

Electromagnetic Spectrum

High Frequency = High Energy = Short wavelength

Label where high frequency, high energy and long wavelength are in your table

Which type of EMR has a frequency of 108? _______________Which type of EMR has a wavelength of 10-13? _______________Which type of EMR has the highest frequency? _______________Which type of EMR has the longest wavelength? _______________Which type of EMR has the highest energy? _______________

Radio waves (television)

Gamma

Gamma

Long wave radio

Gamma

1, 4 and 6

This is because on page 3 of the data booklet, the highest energy EMR is on the right side of the spectrum

2. Which of the following forms of EMR contains photons that possess higher energy than those of ultraviolet radiation?

A. X-rayB. RadioC. InfraredD. Microwave

A. Since X-rays are to the left of UV on the spectrum

1, 2, 6 and 7Wavelengths of 10-5 to 10-9 are infrared, visible and ultraviolet light. Therefore, mosquitoes cannot sense any other types of radiation.

Practice using Page 1 of the data booklet for unit conversions

To convert from the common base unit to anything else, divide by the factor given! To convert any unit to the common base, multiply by the factor given!

The middle!

Or think of it as, If you are moving into the middle, you are multiplying your stuff! If you are moving out of the middle, you will be dividing your stuff!

Practice your conversion skills.a. Convert 25m to micrometers c. Convert 400 nanometers to meters

b. Convert 3 Mm to meters d. Convert 50 m to gigameters

25/10-6 = 25 000 000μm = 2.5 x 107μm

Moving out so we divide by the factor

3 x 106 = 3 000 000m = 3.0 x 106m

Moving in so we multiply by the factor

400 x 10-9 = 0.000 000 4m = 4.0 x 10-7m

Moving in so we multiply by the factor

50/109= 0.000 000 05 Gm = 5.0 x 10-8 Gm

Moving out so we divide by the factor

Calculating Wavelength & Frequency of EMR

• Since all EM waves travel with speed of light c, (3.00 X 108 m/s) in a vacuum we can use c = fλ

The equations for calculating wavelength and frequency of EMR are:

orm/s

mHz

3.00 x 108 m/s

This is on page 3 of the data booklet!!!

Speed of wave (_______)

Frequency (_______) Wavelength

(_______)Speed of EMR in air or vacuum

(____________)

Frequency & Wavelength Problem 1: Find the frequency of an AM band radio wave with a wavelength of 390 m. (Answer: 7.69 x 105 Hz)

λ = 390 m

f = ?

c = fλ

f = 769230.7692 Hz7.69 x 105 Hz

f = 7.69 x 105 Hz

Frequency & Wavelength Problem 2: A cellular telephone operates on a frequency of 800 MHz. Determine the wavelength of the EM wave (Answer: 0.375m)

λ = ?

f = 800 MHz

c = fλ

λ = 0.375m

0.375mWe need to first convert MHz into HzSince we are moving into the middle, we multiply by 106

Radio Waves

• Source: vibration of electrons within electric circuits

• Penetrating ability: Radio waves cannot

penetrate metal so an antenna is sometimes needed

Ex. On a car • When the electric field of a radio wave

hits the antenna, electrons within the antenna vibrate which helps to transmit the signal

• Is it ionizing: No (low impact on the body)

Use page 3 of your data booklet to fill out the range of wavelength and frequency in your table

• Radio waves have the longest wavelengths in the electromagnetic spectrum. These waves can be longer than a football field or as short as a football.

Radio Waves• Applications: Mostly used for

communication • Ex. Cell phones, radios

• AM radio (amplitude modulated) depends on amplitude (height of waves)

• FM radio (frequency modulated) depends on the frequency of waves

• Also for magnetic resonance imaging (MRI)• MRI used to locate tumors

Microwaves • Source: high-frequency vibrations of electrons

within specialized electric circuits• Penetrating ability: Hazardous to humans due

to the high water content of living tissues – Exposure leads to cataracts

• Microwaves can travel though rain, snow, haze and smoke

• Is it ionizing: No (low impact on the body)• Applications: Used for heating food

– Causes water molecules to rotate and change electric fields

• Used in radar, GPS and satellites Watch a movie on how microwaves work.

Infrared – “heat”• Source: Emitted from a hot object

– Ex. Feeling heat from a camp fire• Penetrating ability: Can burn human

tissue • Is it ionizing: No (low impact on the

body)• Applications: Used in motion

detectors, heat seekers, remote controls and other wireless devices– It has been said that mosquitoes can

detect IR and use it to locate prey

Visible Light: What we can see!

• Visible light is only a small part of the EMR spectrum, but it is the only part we can actually see

• What does Roy G. Biv stand for? – Red, orange, yellow, green, blue, indigo,

violet• What colors have the highest

frequency and shortest wavelength?– Blue and purple

• What colors have the lowest frequency and longest wavelength?– Red

Which colour has the highest energy and is the hottest?

Purple

• Source: Light is emitted by objects that are hot, such as the sun, light bulb and a fire

– Light travels in photons (packets of energy)

– Therefore light has both wave and photon characteristics

• The color of an object is not contained within the object; the color is the result of the light which strikes the object and is reflected by it

Visible Light

• Penetrating ability: visible light can penetrate through air as well as the lenses of our eyes – Detected by the rods and cones on the retina of the eye and chlorophyll

within the chloroplast of plants• Is it ionizing: No (low impact on the body)• Applications: visible light allows us to see objects and for

photosynthesis to occur in plants

Visible Light

Element with the highest

energy/hottest ?

D

D has the longest wavelength, because red has the longest wavelength. The hottest would be copper, because blue is the highest energy and has the highest frequency.

Terminology Associated with Visible Light and all types of EMR

When light hits an object the incident wave splits into 1. Reflected wave2. Refracted (transmitted) wave

Reflected light• Reflected light is what

“bounces” off an object • A mirror is a “perfect”

reflector• Barcodes use the idea of

reflection

Angle of incidence = angle of reflection

Law of reflection

30o 30o

60o 60o

Normal

Reflected light

angle of incidence = angle of reflection

Technology that uses reflection

Reflecting telescopes– light is collected by

parabolic mirror & reflected to a focus

Parabolic reflecting satellite “dishes”

– receive weak radio waves from satellites

Total internal reflection

At a critical angle of incidence, no light rays are transmitted through the medium and totally reflected back into the water, this is called

total internal reflection

Applications of Total Internal Reflection• Both binoculars and fiber optics rely on

total internal reflection

Hundreds or thousands of these optical fibers are arranged in bundles in optical cables. The bundles are

protected by the cable's outer covering, called a jacket.

Fiber Optics• The light in a fiber-optic cable travels through the core

(hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding (lining) does not absorb any light from the core, the light wave can travel great distances.

Need to Know More?Check out a detailed description of the

physics of total internal reflection.

Because fiber optics use light it can carry 100X more info and

conserves energy (less signal degradation

compared to copper)

Smaller fiber optic cable on right has over 6 times message carrying capacity of larger copper wire on left.

Fiber optic cable consists of 6-12 fibersEach pair carries 8000 simultaneous messages!!

Refracted lightRefraction is when EMR waves bend when they go from one medium to another

Highlight which ray shows refraction and in another color, the ray that shoes no refraction.

No refraction

Refraction

Refraction (bending)

Cause pools of water to appear more shallow than they are

Each material has its own REFRACTIVE INDEX (n) - amount that light bends

Answer the following questions using the diagram

Although the driver did not turn the steering wheel, the truck changed direction once it was on the muskeg. When asked to explain what happened, the driver said, “The truck can’t go fast through the muskeg.”

1. Determine whether the truck turned toward the normal or away from the normal.

2. Assume that “a change of direction is due to a speed change” can be applied to light rays passing from air into water. Determine whether light slows down or speeds up when passing from air into water. Does it move towards or away from the normal?

Towards the normal

Light will slow down and therefore bend towards the normal as well

• Diffraction is the scattering of a wave as it passes by an obstacle

• This idea can be applied to all EMR, not just light

Diffraction

• This idea can be applied to telescopes – We want to use telescopes that have a larger opening to minimize

diffraction which allows us to observe fine details despite the effects of diffraction

Diffraction

Diffraction of sunlight causes spider webs to look like a rainbow of

colours by creating diffraction spectrums

PolarizationTry the polarizing filter activity and discuss with your partner about what you think polarization is? Where could it be used?

What happens to light as you try each of the above experiments?

Polarization• Recall that EMR is made up of alternating electric and magnetic fields • Polarization means to confine a wave to vibrate only in one direction • We can use filters to block out 1 direction of vibration, but we wouldn’t want

to block out both…why?• An example of polarization is polarized sun glasses

Polarization helps to reduce glare

Answer: C

Diagrams I and IV show refraction (bending) of EMR when it passed through a medium

Answer: A

DPolarization will block out one of the 2 types of fields.

Ultraviolet• Source: very hot objects

– Bees can see UV

• Penetrating ability: UVA and UVB can penetrate the ozone layer. UVC is absorbed by the ozone– May cause abnormally fast cell division

(mitosis) – cancer (melanoma)– UV is ionizing and can kill bacteria by

breaking down DNA– Can also cause aging of the skin

“Tanorexic mom of five Patricia Krentcil - whose ghastly boot-leather skin makes Snooki look like a ghost - was busted for allegedly taking her 5-year-old daughter into a stand-up tanning booth.”

“Krentcil is such a tanatic that she visits the City Tropic Tanning salon on Centre Street in Nutley roughly 20 times a month, workers there told The Post.”

“Officials said that a school nurse noticed the first-degree sunburns on Anna on April 24. That’s when the girl blabbed that her mom had brought her to the salon.”

Ultraviolet• Is it ionizing: Some types of UV

(UVA and UVB)– Anything to the right of visible light in your table is

ionizing

• Applications: UV radiation is used to test for metal stress (aircrafts)– Used in tanning beds– Used to sterilize equipment

X-rays• Source: produced by fast moving electrons

striking a metal target– black holes may give off x-rays naturally

• Penetrating ability: Can penetrate body tissues

• Is it ionizing: Yes, x-rays have dangerous ionizing effects (mutations) – Children are more sensitive to x-rays as

there cells are still dividing • Applications: x-ray of teeth/bones

– Darker parts of the x-ray mean that more x-rays are passing through the tissue

– Radiation therapy

Gamma rays

• Source: emitted from radioactive material– Emitted from stars!!

• Penetrating ability: Can penetrate metal– can cause mutations and cell death

• Is it ionizing: Yes• Applications: Used to sterilize foods in

process known as irradiation– Medical imaging & diagnosing (instead of CT &

MRI)• Tracks cerebral blood flow, volume &

neurotransmitter receptors