Applications of electromagnetic waves

Electric and magnetic fields in an electromagnetic wave travel _________ to the wave direction

Perpendicular

What are the origins of electromagnetic waves?

Electric charges

A wave is polarized in teh direction of the ________

Electric field

What type of wave are electromagnetic waves?

Transverse

A red filter allows only ____ light to pass through

Red

How does a polaroid filter block vertically polarized light?

When a wave vertically polarized passes through, the electrons inside accelerate causing the wave to lose energy

True or false: most light is unpolarized in a specific directino

True

Light that reflects off a surface becomes polarized in the _______ direction as that surface

Same

What is parallax?

How each eye seeing things slightly differently creates what we see

Why are 3D glasses filmed from slightly diferent perspectives?

To recreate two eyes

How does a 3D movie without any 3D glasses look like?

Blurry

Each lens of a pair of 3D glasses is polarized ________ to each other

Perpendicular

When did Heinrich Hertz come up with the idea to send a wireless signal?

Mid to late 1880s

What inspired Hertz to send a wireless signal?

Maxwell’s equations

Who invented the wireless telegraph and when?

Guglielmo Marconi, 1901

The first public trans-Atlantic wireless conversation happened when…?

President Theodore Roosevelt sent a message to King Edward of England

Where can electromagnetic fields not travel?

They can travel anywhere, including space

Curved mirrors can be used to…?

Focus light and magnify an image

What is the purpose of a satellite dish?

Focus and magnify waves

Why do satellite dishes need to be large?

Radio waves are large (compared to other waves)

What is one of the largest radio telescopes ever nuilt?

Arecibo in Puerto Rico

What star cluster did Arecibo send a message to?

Messier 13

What is the “Cosmic Microwave Background”?

Microwave radiation left over from the birth of the universe

What is the largest space telescope ever built?

James Webb Space Telescope

When was the James Webb telescope launched?

December 2021

What radiation does the James Webb telescope detect?

Infrared

What type of waves create the type of sound waves heard in a radio?

Electromagnetic

Humans can hear and make sounds in the _______ range

KiloHertz (kHz)

The frequencies of radio broadcasts are in the ______ range

MegaHertz (MHz)

Amplitude modulation and frequency modulation are both used to…?

Convert kHz sounds into the MHz range for radio broadcasts

What is amplitude modulation?

When the amplitude of the radio wave is varied with the frequency of the sound wave

If a 500 Hz sound is broadcast onto a 1 MHz radio, the amplitude of the radio wave will vary up and down ______ times a second

500

What type of circuit is inside a radio?

RLC

What is frequency modulation?

When the frequency of the radio wave is varied with the frequency of the sound wave

FM gives off a wave with…?

Multiple frequencies added together

How is audio on television transmitted?

FM

How are images on television transmitted?

AM

How did early televisions produce images?

By using a cathode ray tube

Describe how a CRT works

A cathode emits electrons, which are accelerated by voltage to the anode, and then passed through a magnetic field onto a screen where the signal determines the strength and direction of the magnetic field

What creates the light in a CRT?

The collision of electrons onto a phosphorescent screen

How is the magnetic field produced in a CRT?

Coils

Where is television created from on a screen?

From the top left to the bottom right

Why does the creation of television seem instantaneous?

It is far faster than the human eye can percieve

How do most TVs now create images?

With liquid crystal displays

LCDs take advantage of the…?

polarization of light

Describe an LCD

Each pixel has two glass plates where a gooey material not liquid or solid is in between them

What is a more common term for picture element?

Pixel

How are the glass plates in an LCD polarized?

One is vertically polarized and one is horizontally polarized

Why is light still allowed to pass through an LCD, despite polarization?

The fluid nature of the crystal means light is not 100% vertically polarized, even after it passses through the first plate

What happens to an LCD if voltage is applied?

The liquid crystals line up perfectly and no light passes through them

A pixel becoming dark is another way of saying…?

Light cannot pass through the LCD

Every pixel is made up of what three colors?

Red, green, blue

The cones in our eyes are sensitive to what three colors?

Red, green, and blue

What are the primary colors of light?

Red, green, and blue

Red, green, and blue light makes…?

White light

What are the primary colors of ink?

Yellow, cyan, and magenta

What are the primary colors of ink also known as?

Subtractive primaries

Why are the primary colors of light and ink different?

Ink gets color from absorbing light, not emitting it

Why are incadescent lightbulbs rarely used now?

They are not energy efficient

Most energy of incandescent lightbulbs is emitted in the form of…?

Infrared

A phone is powered by what kind of battery (AC or DC)

DC

A wall plug is powered by…? (AC or DC)

AC

What is a semiconductor?

A mix of two materials that are not good conductors by themselves, but can become a conductor together

What happens to the electrons in a semiconductor?

They are pushed to the outer orbital shell

Why were the first LEDs red?

Red has the lowest energy requirement

Name the order of colors that came to LEDs

Red, green, then blue

Why are LEDs more efficient than other lightbulbs?

They only emit visible light

How are semiconductors used in solar panels?

To absorb light

Burglar alarms use _______ detectors

infrared

Solar panels have existed since the….?

Mid-twentieth century

When energy costs are negative, what happens?

People are paid to generate energy rather than paying to receive it

Most satellites are at least partially powered by whwt?

Solar energy

For now, rockets must use what kind of energy to travel outside Earth?

Chemical

What is a light sail?

A refractive sheet of metal that caches light in order to move

What is the main drawback of the light sail?

The kinetic energy it gets is very tiny and weakens as it gets further from the sun

What is the benefit of a light sail?

It requires no chemicals or fuel and could potentially reach high speeds over a long enough time period