Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
13 Cards in this Set
- Front
- Back
|
Positive lens
Also called? Is normally what of what shape? |
-Converging lens
-Focusing lens -Convex |
|
|
What happens to rays hitting the centre of a positive lens?
|
They are not refractd
|
|
|
State the lens formula.
How does one calculate lens power? |
1/f=1/x+1/y
x=object distance y=image distance f=focal lenth Lens power=1/focal length = Dioptre=1/meter D=1/f |
|
|
Positive lens
When is there no image? |
When x=f and when y=infinity
|
|
|
Positive lens
When is there a real image? |
When
f<x<2f, 2f<y<infinity |
|
|
Positive lens
When do virtual images occur? How do they look? |
When a luminous object is placed closer to the lens than its focal length.
Magnified and upright |
|
|
Negative lens
Also called? Usually of what shape? |
Diverging lens
Concave |
|
|
What do we percieve when an object is placed on the other side of a negative lens?
|
A virtual, upright and smaller image.
|
|
|
What is the power of refraction in the:
-Cornea? -Lens? |
-40D
-17-31D |
|
|
What is the near point for an emmotropic eye?
|
0.1 m
|
|
|
What lens type is useful for correcting myopia?
What are the disadvantages? |
Negative lens
-Decrease in image size (2%/D) -Distort and reduce peripheral vision |
|
|
What type of lens is used for treating hyperopia?
What are the disadvantages? |
Positive
-Acts as a magnifier (2%/D) -Appear to have bif eyes |
|
|
A presbyopic person needs what type of glasses when reading?
|
Positive lens
|
