Lens applications

Question 1

The camera

Answer 1

• takes light from a large object and produces a smaller, real image on the camera.
• meaning object must be further than twice the focal length of the lens (beyond 2F’)
• as object changes location, image will change location so it will be somewhere between F and 2F
• image is inverted, real, closer, and smaller

Question 2

The movie projector

Answer 2

• opposite of camera
• takes small object and projects a large, inverted, real, farther, image on screen.
• because image is larger than object, the film must be located between 2F’ and F’.
• because image is inverted, film must be loaded into the projector upside down so when you see movie on screen it is upright
• image is behind 2F

Question 3

The magnifying glass

Answer 3

• simple converging lens with image in front of F’
• no real image produced, at this objects location. refracted rays spread apart, but the human brain extends these rays backwards and produces an enlarged, virtual image located on same side as where object is (virtual)
• makes things larger and keeps it right side up, farther, virtual.
• only works by bringing it closer to object.

Question 4

the eye

Answer 4

retina- light sensitive cells that focus image, convert light signals to electric signal
optic nerve- carry the electric signals to brain
iris- control amount of light that enters
pupil- where light enters
cornea- convergent lens in eye

Question 5

accomodation

Answer 5

• eye muscles called ciliary muscles that can slightly change lens shape
• this changes focal length of lens, allowing objects at different distances to become clear
• healthy eyes can accommodate to near and far objects

Question 6

Hyperopia

Answer 6

• far sighted (cant see nearby objects)
• caused by too small of distance between lens and retina
• use of converging lens fixes it, called positive meniscus

Question 7

Myopia

Answer 7

• near sighted (cant see far)
• diverging lens achieves correction to this called negative meniscus
• too large distance between retina and lens

Question 8

Contact lenses

Answer 8

• placed on cornea

- can correct vision or change colour of eye (reflecting certain colours of light)