P11: Lenses and The Eye Flashcards
Concave (Diverging) Lens
Concave (Converging) Lens
Uses of a convex lens
Magnifying Glass, In a camera to create a clear image of a far off object.
Uses of a concave lens
To correct short sightedness.
Focal Length
The distance from the centre of a lens to where the light rays focus (or, in the case of a concave lens, appear to diverge from.)
Real Image, from a convex lens.
Virtual Image, from a concabe lens
Magnification of an image =
Image height/ Object Height
How to construct a real image/converging lens diagram
How to construct a virtual/Converging lens diagram
How to construct a virtual/Diverging lens diagram
How does a camera work?
What does ‘real is positive’ mean?
Real images are given positive focal lengths in the formula, virtual negative.
1/focal length =
1/distance from object to lens + 1/distance from lens to image
(1/u + 1/v = 1/f)
A diverging lens…
… always gives a virtual image.
Iris
Coloured ring of muscle that controls the amount of light entering the eye.
Aqueous Humour
Transparent watery liquid that supports the front part of the eye.
Cornea
Transparent layer that protects the eye and helps to focus light onto the retina.
Pupil
the central hole formed by the Iris. Light enters the eye through the pupil.
Ciliary Muscles
Attached to the lens by Suspensory Ligaments.The muscles change the thickness of the eye lens.
Eye Muscles
Move the eye in the socket.
Optic Nerve
Carries nerve impulese from the retina to the brain.
Blind Spot
Region of the retina that is not sensitive to light (no light sensitive cells present)
Retina
The light sensitive cells around the inside of the eye.
Vitreous Humour
Transparent jelly-like substance that supports the back of the eye.
Eye Lens
Focuses light onto the retina.
Type of lens (Eye vs Camera)
Variable focus converging lens
Fixed focus convergin lens
Focusing Adjustment (Eye vs Camera)
Ciliary muscles adjust lens position.
Manual adjustment of lens position.
Image produced (Eye vs Camera)
Both real, inverted, magnification less than 1.
Image detection (Eye vs Camera)
Light sensitive cells on the retina
Photographic Film (or CCD sensors in digital camera)
Brightness Control (Eye vs Camera)
Iris controls width of pupil
Adjustment of aperture ‘stop’
Short Sight
An eye that can only focus on near objects.
Corrected with a diverging lens.
Long Sight
An eye that can only see far away objects.
Corrected with a converging lens.
Power of a lens (D (dioptre)) =
1/ focal length (m)
The higher the refractive index of a lens material…
… The flatter and thinner the lens can be.
