AP Physics Mr. Jean February 10 th, 2012

The plan: Diverging Mirrors Lenses

Demo with a diverging mirror: Questions to think about. 1) Can you make and image LARGER using a single diverging mirror? 2) Where have you seen these before?

What is a lens? They are used to collect light from an object and form magnified or reduced images of that object. Lenses are used in eye glasses, cameras, telescopes and microscopes.

Lens Video Clip:

Converging Lenses:

Focal Length: The focal length is the distance f from the lens center to the focus. It can be found by finding the distance between the lens and a piece of paper when the paper has an image of a distant object on it. The image of an object can be located by finding the intersection point of two rays. The parallel ray is bent through the focus. Another ray will pass straight through the middle of the lens. This assumes that the lens is thin and that the rays are close to the center of the lens.

Example:

Diverging Mirrors: A diverging lens will cause rays parallel to the principal axis to radiate from a virtual focus. Rays passing through the center are not deflected.

The Broken Pen Demo The pen is slowly moved across the middle of the glass from a centered position to an off-center position. As the pen is moved across the middle of the glass, an interesting phenomenon is observed.

Focal Point: The focal point is the point in space at which the reflected light meets along the principal axis.

Reflection in Curved Mirrors:

Option #1: Behind C.

Option #2: In front of C.

Concave Mirrors: Two Rules Any incident ray traveling parallel to the principal axis on the way to the mirror will pass through the focal point upon reflection. Any incident ray passing through the focal point on the way to the mirror will travel parallel to the principal axis upon reflection.

Shrinking an object: To shrink an objects image in a concave mirror you must place the object behind the center of curvature point C with reference to the mirror. Awesome amazing diagrams next.

It can be generalized that anytime the object is located beyond the center of curvature, the image will be located somewhere between the center of curvature and the focal point. In such cases, the image will be inverted and reduced in size

Big-a-sizing an object: To increase the size of the objects reflection in a concave mirror you must place the object in front of the center of curvature point C with reference to the mirror. Awesome amazing diagrams next.

In fact, it can be generalized that anytime the object is located between C and F, the image will be located beyond the center of curvature as well. In such cases, the image will be inverted and larger in size than the object.

Option #3:

Beyond the Focal Length: A generalization which can be made about all virtual images produced by mirrors (both plane and curved) is that they are always upright and always located on the other side of the mirror.

In General:

Lens Program: lenses.cfm