Refraction & Lenses Flashcards
Why are lenses important?
they form images of objects
What are lense made of?
transparent material (glass/plastic)
index of refraction > air
What does a “thin” lens mean?
thickness of lens is negligible compared to the radius of curvature
idealization: all rays get focused to a point
Focal length (f) = _____ for an object at infinity
Focal length (f) = image distance (di) for an object at infinity
because 1/do = 1/∞ = 0
thus, di = f
Is the focal length the same on both sides of the lens?
Yes
Converging lenses are thicker or thinner in the center compared to the edges?
thicker in the center than edges
Diverging lenses are thicker or thinner in the center compared to the edges?
thinner in the center than edges
What do converging lenses do?
make parallel rays converge to a point
Describe the image from a converging lens
Real (inverted) image → small or big
Virtual (upright) image → big
Describe the image from a diverging lens
Virtual (upright) image → small
What do diverging lenses do?
make parallel rays diverge
How can you measure the focal length of a lens?
Find the image point (di) for distant objects (like sun) → where rays intersect in ray diagrams
Can eyes focus converging rays?
No.
The eye can see sharp images only if rays diverging from each point on the image enter the eye
What are the 3 rays to draw for lens ray diagrams?
- Enters parallel → refracts through focal point (behind)
- Passes through F’ → parallel to axis
- Passes straight through center of lens
What is the equation for the power of a lens?
P = 1/f
What are the units of power?
D = 1m-1 (inverse meter)
The power of a converging lens is?
+
The power of a diverging lens is?
–
Magnification Equation for lenses & mirrors?
This lens equation
exactly the same as the mirror equation
Lens Sign Conventions
+ f
– f
+ f = converging lens
– f = diverging lens
Lens Sign Conventions
+ do (standard)
object is on the side of the lens from which light is coming
Lens Sign Conventions
+ di
– di
+di = image is opposite side from where light is coming (real image)
–di= same side (virtual image)
Lens Sign Conventions
+ hi
– hi
+hi = upright image
–hi = inverted image
Lens Sign Conventions
+ M
– M
+M = right side up
– M = inverted
What does focuser mean?
converging (+f)
produce real & virtual images
What does scatterer mean?
diverging (-f) → don’t focus things
produce virtual images
Real images appear on which side of a mirror?
LEFT (+di)
Real images appear on which side of a lense?
RIGHT (+di)
