 Light travels in a straight line  Objects emitting light do so in all directions  A light “ray” is a line and arrow representing the directions and straight line path of light.  Technically an object that is emitting light radiates an infinite amount of rays.

 Since light seems to move in straight lines, why not follow a light wave along a straight line path and simply draw the line to represent how the light will behave  This line will be perpendicular to the wave front of the light wave  Light from an object either results because the object is emitting light or light is reflecting from the surface of the object

 An image is a reproduction of an original object that is produced through the use of light  A mirror is any polished surface that exhibits reflection  Reflection is simply the bouncing back of light from any surface

Laws of Reflection: 1.The angle of incidence equals the angle of reflection 2.The incident ray, normal and reflected ray are in the same plane

 A plane mirror provides the opportunity to fool you by making your eye and brain perceive an image.  The image appears to be the same distance behind the mirror as the object is in front of the mirror.  This is called a virtual image because the object is not really there

 If a concave mirror is thought of as being a slice of a sphere, then there would be a line passing through the center of the sphere and attaching to the mirror in the exact center of the mirror. This line is known as the principal axis.  The point in the center of the sphere from which the mirror was sliced is known as the center of curvature and is denoted by the letter C in the diagram

 The point on the mirror's surface where the principal axis meets the mirror is known as the vertex and is denoted by the letter A in the diagram. The vertex is the geometric center of the mirror  Midway between the vertex and the center of curvature is a point known as the focal point (point F in the diagram)

 The distance from the vertex to the center of curvature is known as the radius of curvature (represented by R)  The radius of curvature is the radius of the sphere from which the mirror was cut.  The distance from the mirror to the focal point is known as the focal length (represented by f)  Since the focal point is the midpoint of the line segment adjoining the vertex and the center of curvature, the focal length would be one-half the radius of curvature.

 The focal point is the point in space at which light incident towards the mirror and traveling parallel to the principal axis will meet after reflection

 If a ray traveling parallel to the axis of the mirror strikes the mirror, it will be reflected (thanks to the Law of Reflection) through the focus of the mirror.  If a ray passing through the focus of the mirror strikes the concave mirror, it will be reflected (thanks to the Law of Reflection) parallel to the axis of the mirror.  If a ray of light passes through the center of curvature of the mirror, it will be reflected back through the center of curvature.

 When object is behind focus image is real and inverted

 When object is in front of focus image is virtual and upright If the object is closer than one focal length from the mirror, something surprising happens. As

 A virtual image occurs because the reflected rays diverge  Our brain extrapolates where the rays should meet and “sees” a Virtual Image at that location

 Draw one ray perpendicular to the top of the image and the second to the mirror through the focus on the other side  The top line will reflect as if it was coming from the focus and the bottom line will be reflected parallel to the principal axis

 If you trace both of the reflected lines back through the mirror the “virtual image” will be where the lines intersect  In a convex mirror the image will be upright, and seem farther away (smaller) than it actually is  These mirrors are often used for store surveillance and on rear view mirrors on cars

 Lets try online Lets try online