Optical Instruments Flashcards
What happens when the object is outside F in concave lens (2)
-image is virtual
-reduced but upright
What happens when the object is outside F in convex lens (3)
-image is real
-enlarged or reduced
-inverted
What happens when the object is at F in convex lens (2)
-image formed at infinity
-no P ray
What happens when the object is inside F in convex lens (5)
-No f ray as the ray does not pass focal point
-enlarged image
-example of magnifying glass
-upright
-virtual
Define focal point (2)
-it is a specific point where the parallel rays of light either converge or appear to diverge after passing through or reflecting off an optical instrument
State what is convex lens also called as (1)
-converging
State what is concave lens also called as (1)
-diverging
State the formula focal point (3)
1/ distance from object to lens + 1/distance between image and lens = 1/ focal point
(Di = + for real image , - for virtual)
(Do = + diverges)
State the formula for magnification (3)
M = - (distance between image and lens / distance between object and lens )
Upside down = -
Right way up +
What is the focal length convention for concave and convex lenses (2)
- f is positive for convex lenses
- f is negative for concave lenses
What is the magnification convention for concave and convex lenses (4)
- m is + for upright images
- m is - for inverted images
If m less than one then it is reduced
If m greater than 1 its enlarged
What is the image distance convention for concave and convex lenses (2)
- di is + real images
- do is - virtual images
How does a human eye work (3)
-light passes through the cornea of the human eye
-it is then focused by the variable lens on the retina
-the eye produces a real, inverted image on the retina
How does the human eye look at distanced or nearby objects (3)
-the ciliary muscle’s adjust the shape of the lens to alter at the focus point
-the ciliary muscles tense to focus on nearby objects
-they relax to focus on distant objects
Define near point (1)
-it is the closest point to the eye that the lens is able to focus
Define far point (1)
-it is the furthest point at which the eye can focus
Go over lenses in combination (1)
-
State and explain the concept of nearsightedness (5)
-a near sighted person has a far point that is finite distance away
-objects further away appear blurry
-this is due to the relaxed lens focusing too strongly
-so the image is formed in front of the retina
-after the far point the vision is fuzzy
How to correct nearsightedness (2)
-a diverging lens is used (concave)
-it’s focal length is such that a distant object forms an image at the far point
State the formula for refractive lower
= 1 / focal length
Si unit = m-1
State and explain the concept of farsightedness(5)
- a person who has farsightedness can see the object far away easily
-but cannot focus on closer objects
-because the near point is too far away
-the lens of the eye is not strong enough
-fuzzy vision before the near point
How to fix and correct farsightedness (3)
-a converging lens (convex)
-is used to increase the converging power
-the final image is last the near point
What does the magnifying glass do with the near point (1)
-it moves the near point closer to the eye so the object appears closer and larger
State the formula for angular size (1)
= height of the object / distance from the object to the eye
