# Refraction & Lenses Flashcards

1
Q

Why are lenses important?

A

they form images of objects

2
Q

A

transparent material (glass/plastic)

index of refraction > air

3
Q

What does a “thin” lens mean?

A

thickness of lens is negligible compared to the radius of curvature

idealization: all rays get focused to a point

4
Q

Focal length (f) = _____ for an object at infinity

A

Focal length (f) = image distance (di) for an object at infinity

because 1/do = 1/∞ = 0

thus, di = f

5
Q

Is the focal length the same on both sides of the lens?

A

Yes

6
Q

Converging lenses are thicker or thinner in the center compared to the edges?

A

thicker in the center than edges

7
Q

Diverging lenses are thicker or thinner in the center compared to the edges?

A

thinner in the center than edges

8
Q

What do converging lenses do?

A

make parallel rays converge to a point

9
Q

Describe the image from a converging lens

A

Real (inverted) image → small or big
Virtual (upright) image → big

10
Q

Describe the image from a diverging lens

A

Virtual (upright) image → small

11
Q

What do diverging lenses do?

A

make parallel rays diverge

12
Q

How can you measure the focal length of a lens?

A

Find the image point (di) for distant objects (like sun) → where rays intersect in ray diagrams

13
Q

Can eyes focus converging rays?

A

No.

The eye can see sharp images only if rays diverging from each point on the image enter the eye

14
Q

What are the 3 rays to draw for lens ray diagrams?

A
1. Enters parallel → refracts through focal point (behind)
2. Passes through F’ → parallel to axis
3. Passes straight through center of lens
15
Q

What is the equation for the power of a lens?

A

P = 1/f

16
Q

What are the units of power?

A

D = 1m-1 (inverse meter)

17
Q

The power of a converging lens is?

A

+

18
Q

The power of a diverging lens is?

A

19
Q

Magnification Equation for lenses & mirrors?

A
20
Q

This lens equation

A

exactly the same as the mirror equation

21
Q

Lens Sign Conventions

+ f

– f

A

+ f = converging lens

– f = diverging lens

22
Q

Lens Sign Conventions

+ do (standard)

A

object is on the side of the lens from which light is coming

23
Q

Lens Sign Conventions

+ di

– di

A

+di = image is opposite side from where light is coming (real image)

–di= same side (virtual image)

24
Q

Lens Sign Conventions

+ hi

– hi

A

+hi = upright image

–hi = inverted image

25
Q

Lens Sign Conventions

+ M

– M

A

+M = right side up

– M = inverted

26
Q

What does focuser mean?

A

converging (+f)

produce real & virtual images

27
Q

What does scatterer mean?

A

diverging (-f) → don’t focus things

produce virtual images

28
Q

Real images appear on which side of a mirror?

A

LEFT (+di)

29
Q

Real images appear on which side of a lense?

A

RIGHT (+di)