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1

visible spectrum

visible spectrum—that is, the wavelengths of light we can see—makes up only a tiny part of the full electromagnetic spectrum. (Simply put, the electromagnetic spectrum is a group of different types of radiation. It includes everything from radio waves to microwaves and gamma rays.)

2

That entire visible spectrum section you see at the bottom fits into what?

That entire visible spectrum section you see at the bottom fits into that little space between ultraviolet and infrared.

3

We measure the wavelengths of the visible spectrum in what?

nanometers (nm), or billionths of a meter.

4

the visible spectrum spans only

the visible spectrum spans only a few hundred nanometers.

5

we can see wavelengths ranging from

we can see wavelengths ranging from 380 to 760 nm.

6

ultraviolet wavelengths are shorter than

the visible spectrum

7

, while infrared wavelengths are longer than

the visible spectrum

8

Microwaves and radio and TV waves are longer still than.

the visible spectrum

9

Red is the longest of the

of the wavelengths in the visible spectrum,

10

violet is the shortest

visible wavelength.

11

angle of incidence

If our light wave strikes a highly reflective object, it will bounce off at an angle . We call the angle at which the light wave hits the surface the angle of incidence,

12

angle of reflection.

we call the angle at which it bounces off the angle of reflection.

13

These angles are always the same.

angle of incidence and angle of reflection.

14

normal line

normal line, which is the dotted line in our drawing that runs perpendicular to the surface the light is striking.

15

how we measure the angle of incidence and angle of reflection.

We measure them by calculating their relationship to the normal line,

16

UVC

is completely absorbed by the atmosphere.

17

UVB

is the most damaging to our cells, causing cataracts and skin cancer.

18

UVA

also called black light, causes tanning and thickening of the skin and contributes to cataracts.

19

The protective lenses you’ll recommend in sunglasses block what

both UVB and UVA rays.

20

Snell’s Law.

This law allows us to determine the angle at which light will bend as it passes from one substance to another. All we need to know is the refractive indices of both substances. For instance, if we know the refractive index of air (which is 1) and the refractive index of a polycarbonate lens (1.584), we can figure out exactly how far light will bend as it travels through the lens.

21

Law of Refraction

Light bends toward the normal when it enters a medium more dense than the one it came from.

22

refraction

the bending of light.

23

When we talk about refraction, we’re not talking about what?

When we talk about refraction, we’re not talking about light that bounces (reflects) off a surface. Instead, we’re talking about light passing through a substance, bending as it goes.

24

light slows when ...

light slows when it moves from a less resistant or rarer medium (for instance, air) to a denser medium like water.

25

light travels faster when...

light travels faster when it moves from a denser medium to a rarer medium.

26

light will keep moving in a straight line unless it strikes the new medium at an angle. When this happens, it will do what

it will bend.

27

index of refraction.

index of refraction. The higher the index of refraction of a material, the more the light will bend as it goes through it.

28

why the index of refraction is important

this fact is very important, as it explains why the high-index plastic materials you order will make lenses appear thinner.

29

So what’s an advantage of making lenses from a material with a high index of refraction?

Simple: We can make the lenses thinner, because they’ll bend the light more powerfully.

30

High-index plastic lenses are popular with who

High-index plastic lenses are popular with people with strong prescriptions who want to avoid thick lenses.