Lenses Flashcards
(40 cards)
Lens Definition
A transparent object with at least one curved side that causes light to refract.
What are the terms that are used to describe lenses, as well as mirrors?
Plane, Concave, and Convex
How are lenses different from mirrors?
They have two sides.
True or False: Either side of a lens can be plane, concave, or convex.
True
What is the word used to describe when parallel light rays travel through a lens and spread away from a common point?
They diverge.
What is the word used to describe when parallel light rays travel through a lens and come together to a common point?
They converge.
What do converging lenses have?
One or two convex surfaces and are thicker in the centre than on the edges.
What do diverging lenses have?
One or two concave surfaces and are thinner in the centre than on the edges.
True or False: There is one combination of surfaces that causes light rays to neither converge nor diverge.
True
What happens when light rays enter a piece of glass with a plane surface?
The rays bend toward the normal.
What happens when light rays are on the far side of the glass?
The rays will bend away from the normal by the same amount that they first bent toward the normal.
All rays shift to the side (are laterally displaced) but when they leave the glass, what directions are they travelling in?
The same direction as they entered.
True or False: Because there has been no change in the direction of the rays relative to each other, a piece of glass cannot be considered a lens.
True
Converging Lense Definition
A lens that brings parallel light rays toward a common point.
What is the shape that most easily illustrates how parallel rays are brought together?
A lens that is convex on both sides.
What happens when rays are incident on the surface on the left side of the lens? Thus, what happens next?
They move from a fast medium to a slow medium. The rays refract toward the normals causing the rays to converge slightly.
What happens when the light rays leave the second surface of the lens? Thus, what happens next?
They move from a slow medium to a fast medium, and refract away from the normals. Because of the direction of the normals at this surface, the rays continue to converge.
Diverging Lens Definition
A lens that spreads parallel light rays away from a common point.
What is a good example of a diverging lens?
A lens that is concave on both sides.
True or False: The principal axis of a lens is a straight line that passes through the centre of the lens, normal to both surfaces of the lens, as with mirrors.
True
What happens when rays that are parallel to the principal axis pass through a converging lens?
The rays intersect at a point.
As with a concave mirror, what is this point called?
The Focal Point
What happens after parallel rays pass through a diverging lens?
The rays diverge.
Why are there two focal points for a lens?
Because light can pass through a lens from either side.
