P5.3.2 - Lenses Flashcards
What is the purpose of the lenses?
They refract light passing though them
What is the principal focus?
The point where lights parallel rays meet or appear to meet
What is the focal length?
The distance from the lens to the principal focus
The shorter the focal length…
The more powerful the lens
What is the purpose of the convex lens?
It makes parallel rays passing through it converge (focus) to a point
What is the purpose of the concave lens?
Makes parallel rays passing through it diverge (spread out)
What are the problems with short sightedness?
- Eyes lens is too powerful
- Eyes can only focus light rays from objects nearby
- Eyes cannot focus light from objects far away onto retina, instead focusing rays in front of retina
What are the problems with long sightedness?
- Eyes lens is too weak
- Eyes can only focus light rays from objects far away
- Eyes cannot focus light from objects nearby onto retina, instead focussing rays behind retina
What is a real image?
An image that is formed where light rays meet
What is a virtual image?
An image that is formed where light rays appear to come from
What does upright image mean?
Image is same way up as object
What does inverted image mean?
Image is upside down compared to object
What is the equation for magnification?
Image height / Object height
What are some uses of convex lens?
Magnifying glass, camera, eyes, projector, microscope, telescope
What are some uses of concave lens?
Spy holes in doors, back windows of coaches
