Lights Mirror and Lenses

V. Summary/Synthesis/Feedback

• Reflection is the bouncing of light when it hits a surface.
• Two Laws of Reflection:
• The normal line, incident ray, and the reflected ray lie on the same plane.
• The angle of incidence is equal to the angle of reflection.
• The reversal effect is the inversion of the image from left to right.
• Mirrors at an angle produce multiple images.
• Two Types of Reflection:
• Specular/ Regular Reflection - reflection of light on smooth surfaces such as mirrors or a calm body of water.
• Diffuse/ Irregular Reflection-reflection of light on rough surfaces such as clothing, paper, and the asphalt roadway.
• A curved mirror is a reflecting surface in which its surface is a a section of sphere.

Two Kinds of Spherical Mirrors:

• The Concave Mirror or Converging
• Mirror o The Convex Mirror or Diverging Mirror
• Important Points in Ray Diagramming:
• Center of Curvature, C- the center of the sphere in, which the mirror is part. Its distance from the mirror is known as the radius.
• Vertex, V-the center of the mirror.
• Focal Point/ Focus, F-the point between the center of curvature and vertex. Its distance from the mirror is known as the focal length, f.
• The 'Four Principal Rays' in Curved Mirrors
• The P-F Ray is ray of light parallel to the principal axis, is eflected passing through the principal focus, F (concave mirror), and as if passing through the principal focus, F(convex mirror).
• The F-P Ray is a ray of light passing through F (concave mirror) or directed towards F (convex mirror), is reflected parallel to the principal axis.
• The C-C Ray is ray of light passing through the center of curvature, C (concave mirror) or directed towards the center of curvature, C (convex mirror) reflects back along its own path.
• Mirrors are very smooth surfaces usually made of polished metal or silver-coated glass. People have used mirrors for thousands of years. When the Israelites were constructing the tabernacle, the bronze basin and stand were made from the bronze mirrors donated by the women.

Mirrors come in a variety of types. Some mirrors have a fl at surface while others have a curved surface. Whether a mirror is fl at or curved, the law of refl ection states that light refl ects off the mirror in straight lines at the same angle as the light hits the mirror. This means the incoming angle, called the angle of incidence, equals the angle at which the refl ected ray leaves, called the angle of reflection.

A line drawn perpendicular to the surface of the mirror called the normal, labeled Normal in this diagram, divides the angle formed between the incident ray and the reflected ray into two equal angles.

Plane Mirrors

Plane mirrors are flat mirrors that reflect light. In Bible times, they were made of polished metal. Today, they are more commonly made of glass or plastic coated with a thin film of metal. The image produced by a plane mirror that appears “behind” it is called a virtual image. A virtual image is one that forms where light cannot actually reach. The image appears to be as far behind the mirror as the object is in front of the mirror.

Concave mirrors reflect light rays to a point in space called the focus . The focus is in front of the mirror. If you put a piece of paper there, you could see the image on it. The image formed by a concave mirror is called a real image because it would appear on a piece of paper. The distance from the center of the mirror to the focus is the focal length .

Concave mirrors have many uses. Since they tend to make an object appear larger, they are used in science equipment, such as microscopes, and in dental equipment. Make-up mirrors are concave mirrors. The satellite dishes you see on people’s roofs are shaped like concave mirrors for other electromagnetic waves.

Convex Mirrors A convex mirror is curved like the back of a spoon. The edges of the mirror curve away from you. A convex mirror makes reflected light rays spread out. The green lines in the convex mirror diagram are where the reflected rays are traced backwards. They seem to come to a point behind the mirror, forming a smaller, virtual image.

Lenses offer a way to refract light waves for many different uses. Lenses are smooth, curved pieces of transparent glass or plastic. They are made to cause light rays to form certain kinds of images.

• Light always travels in straight lines.

• Light travels more slowly through glass or plastic than air.

• Light bends when it moves from one substance to another

A convex lens that is thicker and more curved has a shorter focal length than one that is thinner and less curved.

Concave lenses are thinner in the middle than at the edges.