Lenses Flashcards
What is a lens?
A lens is a shaped piece of transparent glass or plastic that refracts light.
Why does light change direction when it hits a wave?
When light is refracted it changes direction due to the change in density as it moves from air into glass or plastic.
Describe a convex lens
A convex lens is thicker in the middle than it is at the edges
What happens to light rays when they enter a convex lens?
Parallel light rays that enter the lens converge. They come together at a point called the principal focus.
How is a convex lens drawn in a ray diagram?
As a vertical line with outward facing arrows to indicate the shape of the lens.
What is the distance from the lens to the principal focus called?
The distance from the lens to the principal focus is called the focal length.
Describe a concave lens
A concave lens is thinner in the middle than it is at the edges
What happens to light rays when they hit a concave lens?
This causes parallel rays to diverge
How is a concave lens represented in a ray diagram?
In a ray diagram, a concave lens is drawn as a vertical line with inward facing arrows to indicate the shape of the lens.
How can the images produced by a lens be?
upright or inverted (upside down compared to the object)
magnified or diminished (smaller than the object)
real or virtual
What are a real and a virtual image?
A real image is an image that can be projected onto a screen. A virtual image appears to come from behind the lens.
What type of image is formed by a convex lens?
The type of image formed by a convex lens depends on the lens used and the distance from the object to the lens.
Image 1 A camera or human eye
Cameras and eyes contain convex lenses. For a distant object that is placed more than twice the focal length from the lens, the image is:
inverted
diminished
real
Image 2 Magnifying glasses
A magnifying glass is a convex lens used to make an object appear much larger than it actually is. This works when the object is placed at a distance less than the focal length. The image is:
upright
magnified
virtual
What type of image is formed by a concave lens?
Image 3 Concave lenses always produce images that are:
upright
diminished
virtual
