Ch 13 Physics

Question 1

What is refraction?

Answer 1

Refraction: the bending or change in direction of light when it travels from one medium to another

Question 2

Explain the wagon analogy with refraction.

Answer 2

Wagon analogy: when a wagon travels from pavement onto sand, the front right wheel slows down, while the front left wheel does not slow down as it is still on the pavement. Thai results in the wagon pivoting about the slower right wheel, causing a change in the wagon’s direction

Question 3

What are the rules of refraction?

Answer 3

The incident ray, the refracted ray and the normal all lie in the same plane (lay on opposite sides of the line that separate the 2 media)

Light bends towards the normal when the speed of light in the second medium is less than the speed of light in the first medium (second medium is more dense than the first medium)

Light bends away from the normal when the speed light in the second medium is greater (second medium is less dense than the first medium)

Question 4

Why does a spoon in a glass of water appear bent?

Answer 4

→ Light coming from the part of the spoon below the water’s surface must travel through the water into air
→ The speed of light increases from water to air so if it hits the water-air boundary at an angle, light will bend away from the normal
→ The human brain perceives light to travel in a straight line, so it will project these light rays backwards to a virtual light source behind the real spoon

Question 5

How is partial refraction and reflection used in a two-way mirror?

Answer 5

→ Partial refraction and reflection is the idea that light can be reflected and refracted at the same time
→ This effect can be enhanced if glass has a special film coating behind it that allows some light to be refracted but a lot of it is reflected.
→ This results in a mirrored surface that you can see through but other cannot

Question 6

How do we see glass?

Answer 6

→ Glass is transparent but we can still see it because it distorts the light we see around it
→ Some of the light gets reflected off the glass
→ Most of the light gets refracted
→ This distortion of light is what allows us to perceive that there is a substance between the source of light and our eyes

Question 7

What is the index of refraction? Give the formulas.

Answer 7

→ the ratio of the speed of light in a vacuum to the speed of light in a medium is n = C/V
→ n is the index of refraction
→ c is the speed of light in a vacuum
→ v is the speed of light in a given medium
→ The index of refraction can also be calculated using the angle of incidence and angle of refraction: n = sin(angle of incidence)/sin(angle of refraction)

→ n is the index of refraction
→ i is angle of incidence
→ R is angle of refraction

Question 8

Explain the process of total internal reflection.

Answer 8

→ Light bends away from the normal when it speeds up at the boundary of two media
→ In this case, the angle of refraction is always larger than the angle of incidence

→ As the angle of incidence increases, so does the angle of refraction until it eventually hits 90 degrees

Question 9

What is the critical angle and total internal reflection?

Answer 9

→ Critical angle: the angle of incidence that results in an angle of refraction of 90 degrees
→ If you increase the angle of incidence past the critical angle the refracted ray will no longer exist in the medium. Instead it will reflect back onto medium
→ The refracted ray disappears, only a reflected ray is visible. This is called total internal reflection.

Question 10

What are the two conditions for total internal reflection to occur?

Answer 10

Light is travelling more slowly in the first medium than in the second

The angle of incidence is greater than the critical angle (no refraction occurs; all light is reflected back into the medium)

Question 11

What is a lens? Give examples.

Answer 11

a lens is an optical device which transmits and refracts light

Ex. telescope, night vision goggles, glasses, microscope, camera, projector

Question 12

Explain the path of light in a lens

Answer 12

→ In a lens, light is refracted twice. Once when going from air to glass and then again when going from glass back to air
→ We are only concerned with the direction of the incident ray entering the lens and the emergent ray leaving the lens
→ Ray diagrams can be simplified by drawing a dashed line through the center of the lens and showing refraction occurring at this lines

Question 13

What is a converging lens and how is it shaped?

Answer 13

Convex Lens and thicket in the middle

→ A converging lens is a lens that is thickest in the middle and that causes incident parallel light rays to converge through a single point after refraction

Question 14

What is the optical center (O)?

Answer 14

→ Optical center (O): the point at the exact center of the lens

Question 15

What is the principal focus (F)?

Answer 15

→ Principal focus (F): the point on the principal axis of a lens where the light rays parallel to the principal axis converge after reflection
→ Because Light can strike from either side of a lens, every lens actually has two foci. To tell them apart, the focus on the same side as the incident light is called the secondary principal focus (F prime)

Question 16

Where is each foci located in a converging lens?

Answer 16

secondary principal focus is located on left of lens and principal focus is located on right of lens

Question 17

What is a diverging lens and how is it shaped?

Answer 17

Concave lens

→ A lens that is thinnest in the middle and that causes incident parallel light rays to spread apart after refraction

Question 18

How are light rays travelling in a diverging lens?

Answer 18

→ Light rays in a diverging lens do not converge but spread apart
→ If you project these diverging rays backwards, it looks as if they come from a virtual focus
→ This point is now the principal focus
→ The secondary principal focus is now on the other side of the lens where the rays actually diverge
→ Note that F and F prime are equally for apart from the optical center of both a converging and diverging lens

Question 19

How do you locate images in a converging lens?

Answer 19

A ray parallel to the principal axis is refracted through the principal focus
A ray through the secondary principal focus will refract parallel to the principal axis
A ray through the optical center continues straight through without being refracted

Question 20

What do you get when an object is beyond F prime in a converging lens?

Answer 20

→ When an object is beyond F prime, we always get a real and inverted image
→ The size and location of the image depend on the location of the object

Question 21

What happens when an object is placed on F prime in a converging lens?

Answer 21

→ When an object is placed on F prime, you get no clear image
→ The refracted rays are parallel and do not cross to form an image, even when extended backwards

Question 22

What happens when an object is placed between F prime and the lens in a converging lens?

Answer 22

→ When an object is between F prime and the lens, you get an upright, virtual image
→ The virtual image is described as being behind the lens because light rays do not actually arrive at the image location, they only appear to

Question 23

How do you locate images in a diverging lens?

Answer 23

A ray parallel to the principal axis is refracted as if it had come from the principal focus (F)
A ray that appears to pass through the secondary principal focus (F prime) is refracted parallel to the principal axis
A ray through the optical center continues straight through on its path

→ A diverging lens always produces the same image characteristics no matter where the object is

Question 24

Give a summary of the SALT charcaterstics in both types of lenses

Answer 24

Converging lens:

Beyond 2F’: smaller, inverted, between F and 2F, real
At 2F’: same size, inverted, 2F, real
Between 2F’ and F’: larger, inverted, beyond 2F, real
At F’: no clear image
Inside F’: larger, upright, behind the lens, virtual
Diverging lens:

Anywhere: smaller, upright, same side as object, virtual

Question 25

What is do?

Answer 25

Do = distance of object, this will always be a POSITIVE number

Question 26

what is di?

Answer 26

Di = distance of image, will be POSITIVE for REAL images (opposite side to object) or NEGATIVE for VIRTUAL image

Question 27

what if f?

Answer 27

F = POSITIVE for CONVERGING lens and NEGATIVE for DIVERGING LENS

Question 28

when do you use thin lens equation?

Answer 28

→ Use the thin lens equation which relates focal length(f), the object distance (do) and the image distance (di)

Question 29

what is ho?

Answer 29

ho = height of object (positive when pointing up for principal axis and negative if pointing downward from principal axis

Question 30

what is hi?

Answer 30

height of image

Question 31

what is M?

Answer 31

M = magnification, positive if image stays on same side of PA and negative if becomes inverted M > 1 = larger image M < 1 = smaller image

Question 32

when do you used magnification equation?

Answer 32

to find size

Question 33

How does light bend when travelin from water into air?

Answer 33

When light travels from water into air, it bends away from the normal line, which is an imaginary line perpendicular to the surface between the two mediums. This bending, called refraction, occurs because light travels slower in water than in air, and the change in speed causes the light ray to change direction.

Question 34

How do we percieve a pencil in water?

Answer 34

Light from the submerged pencil tip reaches your eyes. Your brain then projects the rays backwards in a straight line to create a virtual image in the water. This virtual image is higher than the actual pencil tip, resulting in the pencil appearing to be bent. The pencil tip appears to be at a shallower depth than it really is.

Question 35

What is apparent depth?

Answer 35

The distance from the surface of the water to where the object appears to be (the virtual image) is called the apparent depth Objects under water always appear to be nearer to the surface than they actually are. Apparent depth is an optical illusion. This is what makes fish in water appear to be closer to the surface than they actually are

Question 36

Explain the phenomenon of the flattened sun.

Answer 36

Sunsets offer a unique opportunity to see an unusual image due to refraction. People notice that when the Sun is near the horizon during sunset, it appears to be flattened. When the Sun is close to the horizon, light from the bottom of the Sun is refracted more than light from the top of the Sun. Part of the reason is that air is more dense near Earth’s surface than higher up in the atmosphere. So the increased density of air closer to Earth results in greater bending of the Sun’s rays. In addition, the light rays from the bottom of the Sun have a greater angle of incidence than the light rays from the top of the Sun. This results in the Sun having a flattened appearance rather than its familiar round shape **the denser air near the ground refracts sunlight from the bottom of the sun more than sunlight from the top, making the lower part of the sun appear higher, thus giving the sun an oval or flattened appearance**

Question 37

Explain the phenomenon of a mirage.

Answer 37

The pool of water on a highway is a mirage. A mirage can appear when light is travelling from cool air into warmer air. The index of refraction for air decreases as the air gets warmer. This results in light bending farther away from the normal as the air temperature continues to increase. Eventually, total internal reflection occurs in the lowest (hottest) air layer. The light ray now travels up from the hottest layer to the cooler layer above and is gradually refracted toward the normal as the air temperature decreases. This light ray eventually enters your eyes. A motorist who sees this curved light forms a virtual image on the highway. In reality, the pool of water is a virtual image of the sky on the highway. Because the human brain perceives light to travel in a straight line, the motorist projects the image of the sky onto the highwa

Question 38

Explain the phenomenon of shimmering

Answer 38

As with a mirage, shimmering is caused by light being refracted as it passes through air of different temperatures. At night, the air just above a lake is much warmer than air farther away from the water’s surface. Moonlight passes through layers of air that have different temperatures. In the coldest air layer, light travels more slowly so a light ray going through this layer bends toward the normal. As the light ray continues travelling downward toward the warmest air layer (just above the lake), its speed increases, so the light ray bends farther and farther away from the normal. Eventually, total internal reflection occurs in the lowest warm air layer. This results in multiple virtual images of the Moon on the water’s surface

Question 39

Explain the phenomenon of a rainbow/

Answer 39

The rainbow is an optical phenomenon that is produced by water droplets in Earth’s atmosphere The first step in the process involves refraction as light enters the raindrop (going from air into water), resulting in dispersion. The second step is partial internal reflection when this light hits the back of the raindrop. The third step is refraction as the light now exits the raindrop (going from water into air). This is the light that your eyes see, which you perceive as a rainbow. Your brain projects these light rays backwards and forms a virtual image of the spectrum: a rainbow You can only see a rainbow when the Sun is behind you