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Geometrical Optics

In this section, we study the reflection of light, focusing on how light is reflected in

Law of Reflection

The law of reflection states that the angle of incidence is equal to the angle of reflection. Remember that the angles are measured relative to the normal line.

Virtual Image

Virtual Image is an image formed by light coming from an apparent light source (behind the mirror); light is not coming from the actual image location (actual light source).

 virtual_image

Real images are always on the same side as the object; virtual images are on the other side.

Images in Plane Mirror

plane_mirror_image

Anatomy of Curved Mirrors

A concave or a convex mirror can be thought of as being a slice of a sphere. On the principal axis:

Note: in convex mirror, focal length f is negative by convention.

Concave mirror:

 

Convex mirror:

The Mirror Equation

Suppose

We have:

1/f = 1/So + 1/Si

m = hi / ho = -Si / So

NOTE:

Applying the mirror equation to concave mirrors, there are 5 different scenarios:

Refer to http://www.physicsclassroom.com/class/refln/Lesson-3/Image-Characteristics-for-Concave-Mirrors for more details.

Applying the mirror equation to convex mirrors, there is only 1 scenario: image is virtual, not inverted, and smaller than object.

Applying mirror equation to lens

The above mirror equations can be applied to lens. Assume thin lense approximation, and redefine:

There are 5 scenarios for convex lens:

There is 1 scenario for concave lens: