Lesson 3: Light in Everyday Life, Properties of Light, Properties of Matter, Learning from Light, Telescopes

Question 1

What happens when you put the white light from the Sun through a prism? What happens if you pass it through another prism after that?

define Refraction and Dispersion

Answer 1

Prism (glass triangle)
White light is made up of all the colours - then if you put them in a prism, you’re dispersing the light so you can see the colours

• Refraction: the bending of light as it moves from one medium to another
• Dispersion: the separation of the individual colours into a spectrum

Question 2

What is a spectrum?

Answer 2

colours of light

Question 3

What are some ways light and matter interact?

4 ways

Answer 3

• Emission - emitting light/radiation
• Absorption - light is absorbed and converted into energy
• Transmission - light going through or not going through some medium
  ○ Transparent objects transmit light
  ○ Opaque objects like concrete, block (absorb) light
• Reflection/scattering
  → Reflection: when light bounces in only one direction
  → Scattering - when light bounces in all directions

Question 4

What is electromagnetic radiation?

also, how is the strength of a star encoded in?

Answer 4

radiation composed of both electrical energy and magnetic energy

• Encoded in waves / particles
  → particles of light are called photons

Question 5

What are some defining properties of a wave?

define a wave; wavelength; frequency

Answer 5

Wave: a pattern of motion that can carry energy without carrying matter along with it

Wavelength: is the distance between to wave peaks

Frequency: the number of times you get a peak

Question 6

How does a wave communicate the different types of light to our eyes (ie, what is the difference between blue light and red light? bright light or dim light?

what are the two key terms that determine brightness and colour?

Answer 6

Amplitude determine the intensity of light / the height of the wave
* if the wave length has a higher height, the star is more intense (blue stars are more common for this, not red because of their longer wave lengths)

Wavelength (𝛌) determines the colour of light
* the distance between peaks determine colour, longer are more red, shorter (higher freq.) is blue)

Question 7

What is the electromagnetic spectrum?

Answer 7

The complete range of all types of radiation that has both electric and magnetic fields and travels in waves
* gamma rays, x-rays, ultraviolet, visible, infrared, radio

Question 8

What is a photon?
Fill in blank: The higher the photon energy, the ____ the wave length

Answer 8

Particles of light are called photons
* The higher the photon energy - the shorter the wave length
* Each photon has a wavelength and a frequency

Question 9

What is the speed of light?

(the equation)

Answer 9

λ×f=c
(wavelength λ x frequency f = speed of light c)

Question 10

How is an atom structured? What are its constituents?

Hint: matter is made up of ___

Answer 10

Matter is made up of atoms - which is made up of Proton, neutron, and electrons
→ Protons and neutron surrunding the nucleus outside of it

Question 11

What is the defining feature of each type of element?

For Hydrogen, Helium, and Carbon

Answer 11

Hydrogen - 1 proton
Helium - 2 protons
Carbon - 6 protons
* (same amount of electrons as protons)

Question 12

What is atomic number? what is atomic mass number? Molecule?

Answer 12

Atomic number = # of protons in the nucleus

Atomic mass number = # of protons + neutrons
* same amount of protons as neutrons (EXCEPT for hydrogen)

Molecules: consist of two or more atoms (H2O, CO2)

Question 13

What is an isotope?

Answer 13

Isotope: same number of protons but different number of neutrons (4He, 3He)

Question 14

What is an ‘ground state’ or an ‘excited state’?

Answer 14

Ground state: natural place for electron to hangout / usually at bottom energy level

Excited State: when you give electron more energy, it’ll start moving around / pushed further away from proton into higher energy levels

Question 15

What does ‘ionization’ mean?

Answer 15

If enough energy is absorbed, the electron can be completely removed from the atom (gets way too excited)
* escaped electron

Question 16

Describe how electrons move into different energy levels?

define absorption and emission for atoms

Answer 16

Process called absorption. The electron absorbs the energy and jumps to a higher energy level.
In the reverse process, emission, the electron returns to the ground state by releasing the extra energy it absorbed.

Question 17

What are the three basic types of spectra?

Answer 17

Continuous Spectrum
○ If its providing light in a large range of the spectrum
○ Ex. Sun
○ light coming directly through (no cloud of gas)

Emission Spectrum
○ Sharp spikes of light in a specific spot
○ You only get light in specific places - called emission lines ○ cloud of gas only

Absorption Spectrum
○ Sharp spikes of colours removed from the spectrum - absorption lines
○ Some of the light is absorbed by the cloud of gas
○ light going through cloud of gas

Question 18

How can we measure what something is made of based off just the spectrum?

what is the key term called and how it affects the ‘lines’

Answer 18

Chemical footprints

• When an electron absorbs a photon with the exact energy/wavelength it needs to get excited, the electron jumps to a higher level, causing an absorption line
• When an excited electron drops down a level, it emits a photon with the exact energy/wavelength to return to ground state, causing an emission line

Specific chemicals absorb light differently, so we can tell what chemical (ex. Hydrogen atom) it is

Question 19

What is thermal radiation?

Answer 19

Electromagnetic radiation emitted from a material that is due to the heat of the material
* Nearly all large or dense objects emit thermal radiation, including stars, planets, you

Question 20

How does thermal radiation help us measure the temperature of an object?

1. Hotter objects emit more __ at all ___ per unit area
2. Hotter objects emit ___ with a ___ average ___

what are the two properties? Explain the example for 3000-15,000 K stars

Answer 20

1. Hotter objects emit more light at all frequencies per unit area
2. Hotter objects emit photons with a higher average energy

Looking at the Thermal Spectrum of Stars
* 3000 K Star, cool stars appears more red
○ Red-dwarf is an example of a cool star
* 15,000 K Star, warmer stars appears more blue

Question 21

What is the doppler effect relative to wavelengths?

Answer 21

• The wave length of something changes relative to the velocity
• Higher the frequency, higher the pitch
• The faster something is moving, the more squished the waves are

Question 22

What does blueshift/redshift mean?

Answer 22

1. Light emitted from an object moving toward you will have its wavelength shortened
   ○ BLUESHIFT
2. Light emitted from an object moving away from you will have its wavelength lengthened
   ○ REDSHIFT

Light emitted from an object moving perpendicular to your line of sight will not be shifted

• DOES NOT MEAN STAR HAS A BLUE OR RED TINT

Question 23

How does it help us measure the speed of an object? Using blueshift and redshift..

Answer 23

We generally measure the Doppler effect from shifts in the wavelengths of *spectral lines *
* The amount of blueshift or redshift tells us an object’s speed toward or away from us

Question 24

Name three things telescopes do better than our eyes

Answer 24

1. Telescopes collect more light than our eyes
   → light-collecting area
2. Telescopes can see more detail than our eyes
   → angular resolution
3. Telescopes/instruments can detect light that is invisible to our eyes (eg, infrared, ultraviolet)

Question 25

What are the differences between refracting and reflecting telescopes?

Answer 25

Refracting Telescope: Uses lenses to focus light from a large collecting area to a single point (the focus)

Reflecting Telescope: Uses mirrors to focus light from a large collecting area to a single point (the focus)

Question 26

What is Imaging? what is spectroscopy?

(these are the two ways to collect light)

Answer 26

Imaging - sensitive pixels that collect light and takes a picture

Spectrum - expanding the light into ranges

Question 27

Why are telescopes that measure different types of light (ie,xray,radio,etc) constructed differently?

how it interacts with matter

Answer 27

Different energy wavelengths interact with matter in different ways.
* Radio waves will reflect from a metal that X-rays pass right through.
These differences in the interaction between matter and energy have resulted in telescopes designed to only accommodate very specific wavelengths

telescopes are light collecting buckets, the bigger the bucket, the more light will come in

Question 28

Why do we put telescopes in space?

3 reasons

Answer 28

1. Light Pollution
   → Pollution is the atmosphere will cause the light to bounce as well
2. Turbulence causes twinkling —> blurs images [primary reason]
   → Earth’s atmosphere is made up of water, when light is entering into the atmosphere it’s entering a turbulent fluid
   → Scintillation = the flickering of star light due to atmospheric turbulence
3. Atmosphere absorbs most of EM spectrum, including all UV and X ray and most infrared
   → these rays don’t make it to the ground

Question 29

Describe how we have been able to improve ground-based observing?

(1 key term: Adaptive ___)

Answer 29

Adaptive Optics: Rapid changes in mirror shape compensate for atmospheric turbulence
* laser points to the sky to overcome blurry atmosphere and Scintillation

Question 30

Describe what is meant by the word radiation?

Answer 30

Radiation: term for light waves that radiate outward from the source

Question 31

Describe how Maxwell’s theory explains the generation of a magnetic field? How does this help explain why light can travel through the universe without a medium?

Answer 31

Maxwell described light as a propagating (transmit through a medium) wave of electric and magnetic fields.

generally, he predicted the existence of electromagnetic radiation

Question 32

What does ROY G BIV stand for?

Answer 32

ROY G BIV—for Red, Orange, Yellow, Green, Blue, Indigo, and Violet.

Question 33

How are wavelength and frequency interrelated?

Answer 33

Wavelength (λ) and frequency (f) are related because all electromagnetic waves travel at the same speed

Question 34

What is the inverse-square law? How does it related to the propagation of light?

the apparent _ of a source gets ___ ___ ____ ; how does it relate with gravity

Answer 34

that the apparent brightness of a source (how bright it looks to us) gets weaker with distance

• the propagation of light is similar to the effects of gravity. The force of gravity between two attracting masses is also inversely proportional (both decrease) to the square of their separation.

Question 35

Describe each of the major portions of the electromagnetic spectrum. Provide examples of something that generates that type of light.

Answer 35

Gamma rays: the shortest wavelengths, no longer than 0.01 nanometer
○ generated deep in the interior of stars
○ carry a lot of energy, they can be dangerous for living tissues
○ gamma rays coming to Earth are absorbed by our atmosphere before they reach the ground

X-Rays: wavelengths between 0.01 nanometer and 20 nanometers
○ are able to penetrate soft tissues but not bones, and so allow us to make images of the shadows of the bones inside us

Ultraviolet: higher energy than violet, more energetic than visible light
○ Referred as “blacklight” - eyes can’t see it
○ a small fraction of ultraviolet rays from our Sun do penetrate to cause sunburn or, in extreme cases of overexposure, skin cancer in human beings.

Visible light: wavelengths between roughly 400 and 700 nm, these are the waves that human vision can perceive
○ Visible light penetrates Earth’s atmosphere effectively, except when it is temporarily blocked by clouds

Infrared: longer wavelengths than visible light
○ Infrared waves are absorbed by water and carbon dioxide molecules, which are more concentrated low in Earth’s atmosphere.

Microwave: used in short-wave communication and microwave ovens.
○ are absorbed by water vapor, which makes them effective in heating foods.
○ Radio waves: All electromagnetic waves longer than microwaves

Question 36

What determines the type of electromagnetic radiation emitted by the Sun (or any other dense astronomical object)?

Answer 36

Temperature

Question 37

What is temperature actually measuring (referring to something on the atomic level)?

Answer 37

A gas consists of atoms and/or molecules that are flying about freely at high speed, continually bumping into one another and bombarding the surrounding matter. The hotter the solid or gas, the more rapid the motion of its molecules or atoms.
——-
To simplify, if an object is hot (temperature), the more the molecules will move up energy levels by absorbing so much energy, which will show on the electromagentic specturm

——-

the higher the temperature, the shorter the wavelength at which the maximum power is emitted.
* because the higher the object’s temperature, molecules will keep absorbing more and more energy which is reflected on the spectrum

The temperature of something is thus a measure of the average motion energy of the particles that make it up.

Question 38

What is a spectrometer?

Answer 38

showcases the array of colours is a spectrum of light

Question 39

What is an alpha particle?

Answer 39

(α particles) are helium atoms that have lost their electrons and thus are positively charged.

Question 40

What is deuterium? How is it different from regular hydrogen?

Answer 40

Deuterium is a stable isotope of hydrogen
* unlike “normal” hydrogen atoms, or protium, also contains a neutron

Question 41

Describe what an energy level is, and how it is possible for an electron to move between them

Answer 41

each of the permitted electron orbits around a given atom has a certain energy value, known as energy level

Question 42

What do we mean when we say ‘radial velocity?’

velocity: is the speed of motion; how it affects the Doppler effect

Answer 42

Radial Velocity: the Doppler effect is produced only by a motion toward or away from the observer
* Sideways motion does not produce such an effect.

Question 43

What are the three basic parts of a telescope?

Answer 43

1. Telescope: serves as a “bucket” for collecting visible light (or radiation at other wavelengths
2. An instrument attached to the telescope that sorts the incoming radiation by wavelength
   → Ex. Separate blue light from red light or see spectral lines to determine wat the object is made up of
3. Detector: a device that senses the radiation in the wavelength regions we have chosen and permanently records the observations.