Light and Reflection: Physics

Light and Reflection

• Light is a form of energy which enables sight. This chapter covers reflection and refraction using light properties, specifically straight line propagation.

Reflection of Light

• Reflection is the bouncing back of light from an opaque surface. Most light reflects off highly polished surfaces like mirrors.

Laws of Reflection

• The angle of incidence equals the angle of reflection.
• The incident ray, reflected ray, and the normal to the reflecting surface at the point of incidence all lie in the same plane.

Real and Virtual Images

• A real image can be obtained on a screen.
• A virtual image cannot be obtained on a screen.

Image Formation by Plane Mirrors

• Plane mirrors create virtual and erect images. The image does not form on a screen.
• Images are laterally inverted, where the left side of the object appears on the right side of the image.
• The image size is equal to the object size.
• The image is as far behind the mirror as the object is in front of it.

Spherical Mirrors

• Spherical mirrors have reflective surfaces that are curved inward or outward. There are two types of spherical mirrors: concave and convex.

Concave Mirror

• Concave mirrors are curved inward and are converging mirrors.
• They produce magnified images.

Convex Mirror

• Convex mirrors bulge outward and are diverging mirrors.
• They produce diminished images.

Uses of Concave Mirrors

• Concave mirrors are utilized in torches, searchlights, and vehicle headlights.
• They are also used for shaving mirrors, by dentists for teeth images, and in solar furnaces to focus sunlight.

Uses of Convex Mirrors

• Convex mirrors serve as rear-view mirrors in vehicles because they provide an erect image and help the driver view a large area.
• They are also used as shop security mirrors.

Reflection of Light by Spherical Mirrors

• Spherical mirrors have reflecting surfaces curved inward or outward spherically. A spoon's curved surface can act as a curved mirror.
• A spoon curved inward acts as a concave mirror; curved outward, it acts as a convex mirror.

Terms Related to Spherical Mirrors

• Principal axis: The line joining the pole and center of curvature of the spherical mirror.
• Pole: The geometrical central point of the reflecting spherical surface, denoted by (P).
• Aperture: The width of the reflecting spherical surface.
• Center of curvature: The center of the sphere of which the reflecting surface of a spherical mirror is a part; denoted by (C).
• Radius of curvature: The separation between the pole and the center of curvature.
  • PC = R
• Principal focus: The point on the principal axis where all parallel rays meet after reflection, denoted by (F).
• Focal length: The length between the pole and the principal focus.
  • PF = f

Relationship between Focal Length and Radius of Curvature

• f = R / 2