Lenses Flashcards
Convex sides:
Makes light rays converge together
Concave sides:
Makes light rays diverge apart
Converging lens:
Convex sides
Diverging lens:
Concave sides
What is the cornea:
A clear part of the eye in front of the iris
What is the iris:
The coloured part of the eye, and it is made of muscle
What is the lens:
A clear, oval shaped part of the eye that is behind the iris
What are the suspensory ligaments:
They are attached to the end of the lens and to the ciliary muscles
What is the vitreous humour:
The jelly in the back section of the eye
What is the retina:
A layer of cells on the back of the eye
What are the ciliary muscles:
They are attached to the lens via the suspensory ligaments
What is the blind spot:
The place at the back of the eye where the blood vessels and nerves join the eyeball
What is the optic nerve:
A nerve at the back of the eye that leads to the brain
What is the pupil:
A gap in the iris
How does long-sightedness occur:
The lens in your eye doesn’t focus the light until it is past the retina
How does short-sightedness occur:
The lens in your eye focuses the light before the retina
Define myopia:
Short-sightedness
How do glasses work:
They partially focus the light so your lens focuses the altered light onto the retina
Which type of incorrect sight has a lens too thick:
Short-sightedness
Which type of incorrect sight has a lens too thin:
Long-sightedness
Define object:
What you look at through a lens or optical instrument
Define image:
What you see through a lens or optical instrument
Define upright:
The image is the same way up as the object
Define inverted:
The image is upside down to the object
Define real:
There is no need to extend the rays to find the image
Define virtual:
The rays need to be extended to find the image
To draw ray diagrams side 1:
One parallel, one through the centre of the lens, one connected to the parallel on the other side
To draw ray diagrams side 2:
One from the centre line (doesn’t refract), one parallel, one connected to the parallel on the other side
What is the focal length:
The length between the centre of the lens and the focal point
What is the nature of an image:
Magnified/diminished (for virtual images), real/virtual, upright/inverted
How can you tell the difference between a real and virtual ray diagram that has no extended rays (yet):
A real diagram has the object equal to or longer than the focal length away from the lens on the other side. A virtual diagram is closer than the length of the focal length
How do you find the focal point on a diverging/concave lens:
Extend the rays backwards
Concave lenses are used to treat:
Short-sightedness
Convex lenses are used to treat:
Long-sightedness
Magnification formula:
Image height
Magnification = ―――――――
Object height
What is the unit for magnification:
None, but if one is specified use it
Images formed by concave lenses are always:
Virtual, upright and diminished
