Light & Optics Unit Test Flashcards
Who was Euclid and what was his theory related to light?
Greek
Proposed that light traveled in straight lines and is reflected off of a surface at the same angle that it strikes it.
Who was Pythagoras and what was his theory related to light?
Greek
Pythagoras, best known for the theorem of the right-angled triangle, proposed that vision resulted from light rays emerging from a person’s eye and striking an object
Who was Newton and what was his theory related to light?
English
Newton suggested that when particles of light end up in a medium, such as air or water, they are attracted to the particles of that medium due to an attractive force (gravity) between the particles.
Who was Al-Haytham and what was his theory related to light?
Islamic
Suggested that the eyes receive light reflected from objects, rather than emanating light themselves.
What is an incident ray?
An incoming ray of light
What is a plane mirror?
- Flat mirrors
- Provide the clearest reflections
- We can use them to investigate how reflected light behaves
What is the angle of reflection?
the angle between a reflected ray and the perpendicular to a reflecting surface drawn at the point of contact
What is the normal?
a normal ray is a ray that is incident at 90 degrees to a surface. That is, the light ray is perpendicular or normal to the surface.
What is the EM Spectrum?
EM stands for electromagnetic
In order from lowest to highest frequency they are: radio, microwave, infrared, visible, ultraviolet, x-ray, gamma ray
What is phosphorescent light?
- Some substances have the ability to
store energy when radiation hits them - They can emit light for a long time
after the radiation has stopped - Phosphorescence: ability to emit
light - Example: Glow in the dark items
What is fluorescent light?
- Glass tube filled with a small amount of gas Ex.
Mercury vapour - Inside of the tube is coated with phosphor
Phosphor emits light when exposed to UV
rays - Electricity passes through the tube many times
per second - Every time electricity passes through the gas
emits UV rays - UV rays strike the phosphor and it emits
visible white light
What is bioluminescent light?
- When living organisms produce
their own light - Fireflies have a photophore, a
light producing organ - Light is created by a chemical
reaction - Deep sea organisms like the
angler fish need to create their
own light because the suns rays
do not reach that deep
What are the different optical devices we’ve talked about and their uses?
An optical device is any device that uses light. It could be a mirror (simple) or the Hubble telescope (complex).
Microscope: First microscope is believed to have been built in 1595.
* Combine the power of at least two lenses so you can see great detail
* Two lenses are: Eyepiece and objective
* Light shines through the specimen and a large image is produced by looking through the eyepiece
Telescopes: * Early astronomers used a single lens to get a better look at the stars
* The telescope revolutionized astronomy
* First telescope: 17th century Netherlands
* Telescopes have two characteristics:
– Magnify
– Collect light
Binoculars: * Just two short refracting telescopes!
* Not as powerful as telescopes
* More convenient because they’re smaller
What is the difference between reflecting and refracting telescopes?
REFRACTING TELESCOPE
* Have two lenses, one at each end of a long tube
* Larger objective lens collects light, focuses light on the eyepiece
* In turn you see the image larger than with an unaided eye
REFLECTING TELESCOPE
* Use a large circular mirror
* Mirror is curved so it collects light extremely well
* Another mirror directs the light to the eyepiece
What are some types of mirrors and lenses and what do they do to light?
FUNHOUSE MIRRORS
* Strange imaged produced by flat, inward and outward curved sections of the mirror.
* Mirrors like this have no real practical use
* Single curves in mirrors, however, are useful
CONCAVE MIRRORS
* Surface curves inward like a bowl
* Obey the law of reflection
* Light rays strike on a different point on the curve
* All rays head to a common point, the focal point
* Good at collecting light and bringing it to a single point
* Ideal for reflecting telescopes
* Image formed will depend on how far the object is from
the focal point of the mirror
* Far away= upside down image
* Closer to the focal point = larger the image (still upside
down)
* Object between the focal point = enlarged and upright
CONVEX MIRRORS
* Mirror with a surface curved outward
* Spreads out light rays
* Appears as if the image originates from a smaller point
behind the mirror
* Example: often used on cars
–Often have the warning “Objects in the mirror are
closer than they appear”
CONCAVE LENSES
* Thinner at the centre than the ends
* As parallel rays pass through they are
refracted away from the centre of the lens
* Rays diverge and will never meet on the
other side of the len
CONVEX LENS
* Thicker in the middle than the ends
* As parallel beams of light move through the convex lens
they are refracted towards the centre
* Light rays cross at the focal point of the lens
* Can act as a light collector
* Used in refracting telescopes
* Light rays meet at a point, so we could project them on a
screen
* Problem: image is often upside down
* Image formation depends on how far the object is from the lens
* If the object is past the focal point it will appear upside
down and either smaller or bigger depending on how far
* If the object is between the focal point and the lens it will
appear bigger and upright
What is the relationship between wavelength and frequency?
The more waves you create per second the higher the frequency.
What are the primary colors of light?
Blue, green, red
What are shadows?
- If light hits an object it can’t go through it
- An object between light and our eyes is perceived as a shadow
What is farsighted and nearsighted?
NEARSIGHTEDNESS
* Cannot see distant objects clearly
* The eye cannot make the lens
thin enough to focus light on the
retina
* The image falls in front of the
retina
* Concave lens prescribed
- myopia
FARSIGHTEDNESS
* Cannot see close
objects clearly
* Eye cannot make the
lens fat enough to focus
light on the retina
* Image falls behind the
retina
* Convex lens prescribed
- hyperopia
What is regular and diffuse reflection?
REGULAR REFLECTION
* When light rays hit a smooth surface
* Incoming rays travel parallel to one another
* Hit a smooth surface and all bounce off in the same direction
* The rays stay parallel to each other
* Shinier and smoother the surface the better the reflection
DIFFUSE REFLECTION
* When light rays strike a rough or uneven surface
* Due to the rough surface each light ray is reflected in a different direction
* Reflected rays do not remain parallel
What is refraction?
- When light travels at an angle from one substance to another it bends
- Due to changes in the speed of light
- In a vacuum light travels 300 000km/s
- It’s impossible to move at top speed with particles in the way
What are the 4 basic properties of light?
- Light travels in straight lines.
- Light can be reflected.
- Light can bend.
- Light is a form of energy.
What are digital images?
- Also creates a big image with
small pieces - Digital images are split up into
small elements called picture
elements (pixels) - Each pixel has a coordinate and
a number which are stored by
the computer - The computer can read the
string of coordinates and
numbers to form the picture
Describe the difference between a low energy and high energy wave
Low energy photons (such as radio photons) behave more like waves, while higher energy photons (such as X-rays) behave more like particles.
