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Reflection and Mirrors

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The Law of Reflection

“ The angle of incidence equals the angle of reflection.”

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The Law of Reflection•When light strikes a surface it is reflected.

•The light ray striking the surface is called the incident ray.

•A normal (perpendicular) line is then drawn at the point where the light strikes the surface.

•The angle between the incident ray and the normal is called the angle of incidence.

•The light is then reflected so that the angle of incidence is equal to the angle of reflection.

•The angle of reflection is the angle between the normal and the reflected light ray.

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Incident Ray

Angle of Incidence

Reflected Ray

Angle of Reflection

Mirror

Normal

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The incident ray, normal, and reflected ray are all in the same plane.

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Regular reflection occurs when light is reflected from a smooth surface.

When parallel light rays strike a smooth surface they are reflected and will still be parallel to each other.

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Diffuse reflection occurs when light is reflected from a rough surface. The word rough is a relative term. The surface is rough at a microscopic level. For example, an egg is a rough surface. When parallel light rays strike a rough surface, the light rays are reflected in all directions according to the law of reflection.

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Concave mirrors are made from a section of a sphere whose inner surface was reflective.

Concave mirrors are also known as converging mirrors since they bring light rays to a focus. They are typically found as magnifying mirrors

Convex mirrors are made from a section of a sphere whose outer surface was reflective.

Convex mirrors are also known as diverging mirrors since they spread out light rays. They are typically found as store security mirrors.

Types of Mirrors Convex

Concave

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Plane Mirrors have a flat surface. The mirror hanging on the wall in your bathroom is a plane mirror.

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Real images are images that form where light rays actually cross.

In the case of mirrors, that means they form on the same side of the mirror as the object since light can not pass through a mirror.

Real images are always inverted (flipped upside down).

Virtual images are images that form where light rays appear to have crossed.

In the case of mirrors, that means they form behind the mirror.

Virtual images are always upright.

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Plane Mirror

In a plane mirror the object is the same size, upright, and the same distance behind the mirror as the object is in front of the mirror.

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Images in a plane mirror are also reversed left to right.

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The center of curvature also known as radius of curvature (C) of a curved mirror is located at the center of the sphere from which it was made.

The principle axis is a line that passes through both the center of curvature (C) and the focal point (f) and intersects the mirror at a right angle.

C = 2f

The focal point (f) is located halfway between the mirror’s surface and the center of curvature.

Curved Mirrors

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fC

Principle Axis

Concave Mirrors

Light source

Convex Mirrors

f C

Principle Axis

Light source

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Rules for Locating Reflected Images

1. Light rays that travel through the center of curvature (C) strike the mirror and are reflected back along the same path.

2. Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through the focal point (f).

3. Light rays that travel through the focal point (f), strike the mirror, and are reflected back parallel to the principle axis.

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All three of these light rays will intersect at the same point if they are drawn carefully. However, the image can be located by finding the intersection of any two of these light rays.

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Locating images in concave mirrors

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Concave Mirror with the Object located

beyond C

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Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path.

Concave Mirror

Object beyond C

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Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through

the focal point (f).

Concave Mirror

Object beyond C

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Light rays that travel through the focal point (f), strike the mirror, and are reflected back

parallel to the principle axis.

Concave Mirror

Object beyond C

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Concave Mirror

Object beyond C

Image:

Real

Inverted

Smaller

Between f and C

The image is located where the reflected light rays intersect

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Concave Mirror with the Object located at C

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Concave Mirror

Object at C

Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through

the focal point (f).

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Concave Mirror

Object at C

Light rays that travel through the focal point (f), strike the mirror, and are reflected back

parallel to the principle axis.

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Concave Mirror

Object at C

Image:

Real

Inverted

Same Size

At C

The image is located where the reflected light rays intersect

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Concave Mirror with the Object located between f and C

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Concave Mirror

Object between f and C

Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path.

f C

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Concave Mirror

Object between f and C

Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through

the focal point (f).

f C

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Concave Mirror

Object between f and C

Light rays that travel through the focal point (f), strike the mirror, and are reflected back

parallel to the principle axis.

f C

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Concave Mirror

Object between f and C

Image:

Real

Inverted

Larger

Beyond C

The image is located where the reflected light rays intersect

f C

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Concave Mirror with the Object located at f

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Concave Mirror

Object at f

Light rays that pass through the center of curvature hit the mirror and are reflected back

along the same path.

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Concave Mirror

Object at f

Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through

the focal point (f).

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Concave Mirror

Object at f

No image is formed.

All reflected light rays are parallel and do not cross

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Solar "Death Ray":

• http://www.youtube.com/watch?v=TtzRAjW6KO0

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Concave Mirror with the Object located between f and the

mirror

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Concave Mirror

Object between f and the mirror

Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path.

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Concave Mirror

Object between f and the mirror

Light rays that travel through the focal point (f), strike the mirror, and are reflected back

parallel to the principle axis.

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Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through

the focal point (f).

Concave Mirror

Object between f and the mirror

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Concave Mirror

Object between f and the mirror

Image:

Virtual

Upright

Larger

Further away

The image is located where the reflected light rays intersect

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Locating images in convex mirrors

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Convex Mirror with the Object located

anywhere in front of the mirror

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Light rays that travel through the center of curvature (C) hit the mirror and are reflected back along the same path.

Convex Mirror

Object located anywhere

f C

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Light rays that travel parallel to the principle axis, strike the mirror, and are reflected back through

the focal point (f).

Convex Mirror

Object located anywhere

f C

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Light rays that travel through (toward) the focal point (f), strike the mirror, and are

reflected back parallel to the principle axis.

Convex Mirror

Object located anywhere

f C

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Convex Mirror

Object located anywhere

Image:

Virtual

Upright

Smaller

Behind mirror, inside f

The image is located where the reflected light rays intersect

f C