Chapter 18.1- the ray model of light

Question 1

When does the ray model of light take place?

Answer 1

When the apertures through which the light passes through are larger than about 1mm. If smaller than this it moves to diffracting, which is the wave model of light.

Question 2

What is a light ray?

Answer 2

A line in the direction along which energy of light is flowing.

Question 3

Do light rays affect or interact with each other?

Answer 3

No.

Question 4

What stops a light ray from traveling on for forever?

Answer 4

If it interacts with matter

Question 5

What are the four ways in which light interacts with matter?

Answer 5

It can either be reflected, refracted(or both), or be scattered or absorbed.

Question 6

Can light rays cross through each other?

Answer 6

Yes. Because light rays do not interact and are not affected by one another, two rays can cross without either being affected in any way.

Question 7

When a light ray is stopped by matter, how does this matter affect the light ray?

Answer 7

It can cause it to change directions or to be absorbed

Question 8

Where exactly can light be scattered or absorbed?

Answer 8

Within a material

Question 9

Where exactly can light be either scattered or absorbed?

Answer 9

At an interference between two materials

Question 10

What is the source of light rays?

Answer 10

Objects

Question 11

Where do light rays originate from objects and where do the rays get sent?

Answer 11

Rays originate from EVERY POINT on an object.

EVERY POINT on this object sends rays in ALLLL directions

Question 12

What does it mean if an object is self-luminous?

Answer 12

That they directly create light rays. Self-luminous objects include light bulbs and the sun

Question 13

Are all objects self-luminous?

Answer 13

No. If they’re not self-luminous, then they are reflective objects that reflect only rays that originate elsewhere

Question 14

How do eyes see an object?

Answer 14

Eyes can see an object when diverging bundles of rays from each point on the object enter the pupil and are focused to an image on the retina

Question 15

What are reflective objects?

Answer 15

Objects that reflect rays originating from self-luminous objects. These objects include a piece of paper or a tree.

Question 16

What is a ray source?

Answer 16

There are actually no true ray sources, because light rays are actually an idealization.

Question 17

What is the closest true ray source we can get to?

Answer 17

A thin beam of a laser is often a good approximation of a single ray

Question 18

What is a point source?

Answer 18

It is an idealized source of light. It is infinitely small and emits light rays in every direction. The tiny filaments of light bulbs approximate point sources

Question 19

What 4 things are considered self-luminous objects?

Answer 19

1. A ray source
2. A point source
3. An extended source
4. A parallel-ray source

Question 20

What is an extended source?

Answer 20

This is the most common light source. The ENTIRE SURFACE of an extended source is luminous, so that EVERY POINT of an extended source acts as a point source.
Light bulbs, flames, and the sun are extended sources

Question 21

What is a parallel-ray source?

Answer 21

Certain sources, such as flash-lights and movie projectors, produce a bundle of parallel rays. Rays from a very distant object, such as a star, are very nearly parallel.

Question 22

In reality where do rays originate from?

Answer 22

from EVERY point on an object and travel in ALL directions

Question 23

What is a ray diagram?

Answer 23

A diagram that shows a few light rays in order to simplify the situation

Question 24

In order for our eyes to see an object….?

Answer 24

Rays from that object must enter the eye

Question 25

Why wouldn’t you be able to see a laser beam traveling across the room?

Answer 25

Because no light from the laser enters the eye. The beam is invisible to you. This is the case for a ray or a parallel ray source

Question 26

Why are point sources and extended sources visible to all observers?

Answer 26

Because a point/extended source emit rays in every direction, and some of the rays will enter the eye no matter where it is located

Question 27

What is a diffuse reflection?

Answer 27

The process of reflecting incident light in all directions

Question 28

What is scattering?

Answer 28

The process in which single rays are broken into many weaker rays that leave in all directions

Question 29

How are you able to read a book?

Answer 29

When reading a book, every point on the surface of the page is struck by a ray from a lamp. Then, because of diffuse reflection, these rays scatter in every direction, some of which enter the eye

Question 30

Remember that you can’t see laser beams traveling across the room. Now. Tell me. How would you be able to change this so that you could see it?

Answer 30

Lasers can become visible when small particles, such as dust, smoke, or water droplets, scatter the rays from the laser in every direction. Some of the scattered rays are scattered in the direction of your eye, making the particles in the path of the laser visible.

Question 31

First of all Miranda. Define opaque.

Answer 31

It’s an adjective. It means you are not able to see through it. It is not transparent

Question 32

Where does an opaque object intercept rays from and what does it leave behind?

Answer 32

An opaque object can intercept rays from a point source, leaving a dark area, or shadow, behind it

Question 33

What does the shadow of a point source look like?

Answer 33

The shadow is completely dark and the edges of the shadow are sharp

Question 34

Which points cast a shadow for an extended source?

Answer 34

Because EVERY point on an extended source acts as a point source, each of these points also cast a shadow.

Question 35

What do the shadows look like for an extended source?

Answer 35

The shadows from every point overlap. This makes it so the overall shadow is no longer sharp.