Optics Flashcards
Luminous
• luminous objects create their own light
• Natural sources
-produced without human intervention
-ex. sun, fireflies
• Artificial sources
-produced and controlled by humans
-ex. neon signs, flashlight, tv screen
Non-Luminous
• do not create their own light
• e.g., moon, metal, diamond
What is light?
• a ‘piece’ of light energy is called a photon
• light travels very fast and in straight lines
• light does not require a medium (a medium is any substance that energy can be transferred through) it is transferred through radiation (and can travel through a vacuum)
Incandescence
• light is produced due to high temperatures
• ex. burning candle, light bulb
Electric Discharge
• light is produced when an electric current passes through a gas (which causes the gas to glow)
• ex. lightning, neon signs
Phosphorescence
• light produced when phosphors absorb UV light, store some energy and release visible light over and extensive period of time
• ex. glow-in-the-dark
Fluorescence
• an object absorbs UV light and released visible light immediately
• ex. some laundry detergents, highlighters, lights
Chemiluminescence
• light produced by a chemical reaction
• gives off no heat
• ex. glow stick
Bioluminescence
• when chemiluminescence occurs in living organisms
• used by many organisms to protect themselves from predators, to lure prey or attract mates
• ex. firefly
Triboluminescence
• light produced by friction (scratching, crushing or running) between certain crystals
• ex. rubbing two quartz together, wintergreen mints
Properties of light
• when light strikes matter, it can be
• transmitted- light passes through a substance
• reflected- light bounces off an object
• absorbed- light is absorbed by abject and converted to heat
Matter classified as:
Transparent, Translucent, and Opaque
Transparent
• Transmits all or almost all incident light, object can clearly be seen through material
• Ex. glass
Translucent
• Transmits some incident light but absorbs or reflects the rest, objects are not clearly seen through material
• Ex. frosted glass
Opaque
• Does not transmit any incident light, objects are not seen through material
• Ex. textbook
Terminology of Reflection
The normal always forms a 90 degree angle with the mirror and the angle of incident and angle of reflection are always measured to the normal
-Look at diagram
Light Reflecting off Surfaces
• Specular Reflection: reflection of light off a smooth surface (ex. mirror)
• Diffuse Reflection: reflection of light off a rough surface (ex. moving water)
-angle of incident still equals angle of reflection but the normal is at a different angle for each ray
Locating Images in a Concave Mirror (converting): part 1
• concave mirrors are curved “in”
• the principal axis is a line drawn through the centre of the mirror “perpendicular” with the the centre of the mirror
• F= the focal point where, reflected rays meet when incident rays are parallel to the principal axis
• C= the centre of curvature (twice as far from the mirror as “F”)
• V= vertex (midpoint) of the mirror
Locating Images in a Concave Mirror (converging): part 2
- A light ray parallel to the principal axis will reflect through the focus
- A light ray through the centre of curvature is reflected back onto itself
- A ray through F will reflect parallel to the principal axis
- A ray aimed at the vertex will follow the law of reflection (angle of incidence equals angle of reflection)
Locating Images in a Concave Mirror (converging): part 3
To determine the image of an object in front of a concave mirror you need to draw at least 2 incident rays from the top of the object. These rays will be reflected off the mirror and might cross to form and image. Draw the real image where the rays intersect. You will discover that the characteristics of an image (SALT) formed in a concave mirror depend on the location of the object
SALT
Size, Attitude, Location, and Type
Look at examples
Convex
Mirrors (diverging): part 1
• convex mirrors bulge out in the center
• they will always form virtual images that’s are smaller then the object
• light rays have the same properties as a concave mirror, however F and C are inside of a convex mirror
Convex Mirrors (diverging): part 2
- A ray parallel to the principal axis: draw an imaginary line in the mirror towards F and extend the line on the other side of the mirror, this is the real reflection of the light
- A ray towards F will reflect off of the mirror parallel tot the principal axis, extend the reflection to make an imaginary ray in side the mirror, where the two imaginary rays meet is the location of the image
How does the location of the object affect the image in a convex mirror?
• the closer the object is to the mirror, the larger the image will be
• the closer the object is to the mirror, the closer the image will be
Refraction: part 1
• a medium is any substance that light is travelling through
• when light travels from one medium to another it will bend (change direction) this bending is called refraction
• the incident ray is the ray headed towards the new medium
• the normal is an imaginary line perpendicular to the boundary of the two mediums
Refraction: part 2
• the angle of incident is the angle between the normal and the incident ray
• the refracted ray is the ray after crossing the boundary between the two mediums
• the angle of refraction is the angle between the refracted ray and normal
• total internal reflection is when the angle is greater than the critical angle
Refraction: part 3
• refraction happens because of the change in the speed of light in each medium
• the slower the light is travelling, the closer to the normal it will be (slower = closer; faster = further)
• depending on the mediums, some of the light may be reflected as well this is called partial reflection
Refraction: part 4
• light bends towards the normal when it slows down, and away from the normal when it moves quicker
• when the light entering a faster medium (bending away from the normal) it might approach the boundary in a way that the angle of refraction is 90 degrees
• we call this angle of incidence (C) the critical angle
• any larger angle of incidence will result in a total internal reflection
Far-Sightedness (Hyperopia)
• difficulty seeing near objects
• when light focuses behind the retina~ blurred vision
• one reading for this is because the eye is small or short. Converting lenses fix this problem by causing the light rays to converge before reaching the eye
Near- Sightedness (Myopia)
• difficulty seeing far objects
• when the eye brings light to a focus in front of the retina~ blurred vision
• this could happen because the eye is elongated. Diverging lenses fix this problem by causing the light rays to spread apart before reaching the eye
