Optics

Question 1

Luminous

Answer 1

• 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

Question 2

Non-Luminous

Answer 2

• do not create their own light
• e.g., moon, metal, diamond

Question 3

What is light?

Answer 3

• 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)

Question 4

Incandescence

Answer 4

• light is produced due to high temperatures
• ex. burning candle, light bulb

Question 5

Electric Discharge

Answer 5

• light is produced when an electric current passes through a gas (which causes the gas to glow)
• ex. lightning, neon signs

Question 6

Phosphorescence

Answer 6

• 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

Question 7

Fluorescence

Answer 7

• an object absorbs UV light and released visible light immediately
• ex. some laundry detergents, highlighters, lights

Question 8

Chemiluminescence

Answer 8

• light produced by a chemical reaction
• gives off no heat
• ex. glow stick

Question 9

Bioluminescence

Answer 9

• when chemiluminescence occurs in living organisms
• used by many organisms to protect themselves from predators, to lure prey or attract mates
• ex. firefly

Question 10

Triboluminescence

Answer 10

• light produced by friction (scratching, crushing or running) between certain crystals
• ex. rubbing two quartz together, wintergreen mints

Question 11

Properties of light

Answer 11

• 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

Question 12

Matter classified as:

Answer 12

Transparent, Translucent, and Opaque

Question 13

Transparent

Answer 13

• Transmits all or almost all incident light, object can clearly be seen through material
• Ex. glass

Question 14

Translucent

Answer 14

• Transmits some incident light but absorbs or reflects the rest, objects are not clearly seen through material
• Ex. frosted glass

Question 15

Opaque

Answer 15

• Does not transmit any incident light, objects are not seen through material
• Ex. textbook

Question 16

Terminology of Reflection

Answer 16

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

Question 17

Light Reflecting off Surfaces

Answer 17

• 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

Question 18

Locating Images in a Concave Mirror (converting): part 1

Answer 18

• 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

Question 19

Locating Images in a Concave Mirror (converging): part 2

Answer 19

1. A light ray parallel to the principal axis will reflect through the focus
2. A light ray through the centre of curvature is reflected back onto itself
3. A ray through F will reflect parallel to the principal axis
4. A ray aimed at the vertex will follow the law of reflection (angle of incidence equals angle of reflection)

Question 20

Locating Images in a Concave Mirror (converging): part 3

Answer 20

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

Question 21

SALT

Answer 21

Size, Attitude, Location, and Type

Look at examples

Question 22

Convex
Mirrors (diverging): part 1

Answer 22

• 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

Question 23

Convex Mirrors (diverging): part 2

Answer 23

1. 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
2. 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

Question 24

How does the location of the object affect the image in a convex mirror?

Answer 24

• 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

Question 25

Refraction: part 1

Answer 25

• 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

Question 26

Refraction: part 2

Answer 26

• 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

Question 27

Refraction: part 3

Answer 27

• 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

Question 28

Refraction: part 4

Answer 28

• 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

Question 29

Far-Sightedness (Hyperopia)

Answer 29

• 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

Question 30

Near- Sightedness (Myopia)

Answer 30

• 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