Mirror and Lenses

A flat, smooth mirror is called a plane mirror.

Greek Mythology tell the story of Narcissus. He noticed his image in a pool of water and fell in love with himself.

Hence the term a narcissus.

If the surface of a mirror is curved inward it is called a concave mirror.

The image that is formed by a concave mirror changes depending on where the object is located relative to the focal point of the mirror.

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The optical axis is an imaginary straight line drawn perpendicular to the center of the mirrors surface.

The place where all the light rays meet when reflected back on the mirror is called the focal point.

The distance from the center point of the mirror to the optical axis is called the focal length.

A mirror that curves outward like the back of the spoon is called a convex mirror.

Convex mirrors have a wide field of view. The light rays spread apart after they are reflected.

The rays never meet so the image is a virtual image and is smaller than the actual object.

Images Formed by Mirrors

Mirror ShapePosition of

Object Virtual/RealImage Created Upright/Upside

DownSize

Plane Virtual UprightSame as object

Concave

Object more than two focal lengths from mirror

Real Upside downSmaller than object

Object at focal point

Non None None

Object within focal length Virtual Upright

Larger than object

Convex Virtual UprightSmaller than object

Convex lenses are thicker in the middle than at the edges.

A convex lens focuses light rays at a focal point.

A light ray that passes straight through the center of the lens is not reflected.

A concave lens is thinner in the middle and thicker at the edges.

The light rays that pass through a concave lens bend outward away from the optical axis. The rays spread out and never meet at a focal point, so they never form a real image.

Images formed by Lenses

Lens ShapeLocation of

ObjectType of Image

Virtual/Real Upright/Inverted Size

Convex

Object beyond 2 focal lengths from lens

Object between 1 and 2 focal lengths

Object within 1 focal length

Real

Real

Virtual

Inverted

Inverted

Upright

Smaller than object

Larger than object

Larger than object

ConcaveObject at any position

Virtual Upright Smaller than object

The cornea and lens in you eye focus light rays so that a sharp image is formed on the retina.

Refracting telescopes uses two convex lenses to gather and focus light from distance objects.

Light from a distant object passes through an objective lens and an eyepiece lens in a refracting telescope. The two lenses produce a large virtual image.

A reflecting telescope uses a concave mirror, a plane mirror and a convex lens to collect and focus light from distance objects.

Reflecting telescopes use two mirrors to create a real image, which then is magnified by a convex lens.

The Hubble Telescope was launched from the Discovery Space Shuttle in 1990. It has produced images much sharper and more detailed than the largest telescope on the Earth can.

A microscope uses two convex lenses to magnify small objects.