Optics

What is Optics?

– the study of how light behaves, or– the collection and use of light to create images.

• Optical system: Collects light and uses refraction and reflection to form an image– lenses-which refract (bend) light– mirrors - which reflect (bounce) light

How can it bend?

• Light always travels in a straight line, but if it encounters another object or medium, it can change directions.– when light is bent so that it comes together it is

called converging

– when light is bent so that it spreads apart it is called diverging

Light Rays

• an imaginary arrow that follows a single beam of light

Bending of light that occurs when light crosses a boundary between two different substances.

Objects or waves “bounce” off a surface

Images• A place where many light rays from the same point on

an object meet together again in a point called the focus, or focal point.

– They are “pictures” of objects Two types of images:

– virtual - "not real" - the image only seems to be where it is; cannot be projected onto a screen

– real -can be projected onto a screen, because the light actually passes through the point where the image appears

Optical Devices

• Most optical devices have two functions: 1. They collect light rays

2. They bend the collected rays to form an image.

• To illustrate how an optical device works, we draw ray diagrams to trace several light rays through a system

Two rules:

1. In through the focal point, out parallel

The Ray Diagram

2. In parallel, out through the focal point.

Ray diagrams• Help answer questions like:

– Where is the focal point (or is there one)?– Will the image be magnified or reduced in size?– Will the image be upside down or right side up?– Will the image be inverted left or right?

Law of ReflectionLight rays bounce off a mirror at the same angle at

which they arrive.

–plane - flat– image is right-side-up, the same size and virtual

–concave - curved inward; creates a focal point

–if the object is placed at the focal point, the image is inverted, smaller, and real–if the object is placed closer to the mirror the image is larger and virtual

–convex - curved outward–the image is right-side-up, smaller, and virtual–objects appear farther away than they actually are

Three Types of Mirrors

Lenses

a transparent material that refracts light

usually made of glass or plastic with one or two curved surfaces

Bending of light that occurs when light crosses a boundary between two different substances.

–convex converging–- thicker in the center than at the edges–converges the light rays (forms a focal point)–forms a real image (magnifies objects)–corrects farsightedness

–concave diverging–thicker at the edges and thinner in the center–diverges the light rays–images are smaller and right-side-up–forms virtual images–corrects nearsightedness

Two types of lenses: