Lenses Flashcards
What are lenses?
Lenses are devices used to change direction of light by refraction. These also focus light
What is a converging lens?
One which brings light rays together, making them focus onto one point
What is a diverging lens?
One which spreads the light rays out
Rays hit the lens……
perpendicular to lens but parallel to principal axis
What is a lens axis?
A line going through the lens vertically
What is a principal axis?
A line going through the lens horizontally
What is a principal focus?
a point onto which the light rays converge
What is a focal plane?
A plane parallel to the principal focus?
Where do light rays that weren’t perpendicular to the lens go
somewhere else on the focal plane
What does a converging lens look like?
cave outward
What is a focal length?
distance from lens axis to the focal plane
Focal length is positive for?
real images - converging lens
What is a focal length negative for?
virtual images - diverging and converging
What does a diverging lens look like?
Caves inwards
What is the principal focus on a diverging lens?
a point from which the light rays appear to have come from (as long as they’re parallel)
Images created by lens can be …
real and virtual
What is a real image?
the light rays are actually there and can be captured on a screen. A real image is defined as one that is formed when rays of light are directed in a fixed point.
a converging lens can create both…
real and virtual images
What is a virtual image?
light rays aren’t where they appear to be, so image cannot be captured on screen
If the object is further than the focal length away from lens then what image is formed?
real image
What about if closer?
virtual image
does a diverging lens ever form a real image?
None
lens equation
1/u + 1/v = 1/f where f = focal length u = distance to lens axis from object v = distance from image to principal focus (this is negative for virtual images)
What is the power of the lens?
lens ability to bend light. measured in dioptres.
greater power means more refraction
Equation for power?
1/ focal length
when do lenses work together?
when in series - pt = p1 + p2 +p3
What is the equation for magnification?
m = v/u
where
v = image height or v
u = object height or u
