LIGHT PART I
Reflection of Light from Curved Mirrors Types of curved mirrors
<> Convex (diverging mirror)
<> Concave (converging mirror)
Terms used in curved mirrors
Consider the diagram below when two curved mirrors are joined
AB = Convex mirror while ST = Concave mirror
C = centre of curvature
L = pole of the Concave mirror while K = pole of the Convex mirror
CL and CK are radii of curvature of Concave mirror and convex mirror respectively
CL and CK are principal axes of Concave and Convex mirror respectively
Centre of Curvature: Is the centre of the sphere in which the mirror is a part. Radius of Curvature: Is the distance or length between the pole of the curved mirror and the centre of curvature.
Principal Axis: Is the line joining the pole of the curved mirror and the centre of curvature.
Consider when light is reflected in curved mirrors as shown in the diagrams below.
Principle Focus, F: Is the point in which the light is reflected in curved mirror
Focal Length, f Is the distance between pole of the curved mirror and the principal focus. NB: Given that focal length is always half the radius of curvature. Location of Image using Ray diagrams
The following are the rules used to locate image in the curved mirror.
A ray of light travelling to the mirror parallel to the principal axis, a ray is reflected through the principal focus
A ray of light travelling to the mirror through the centre of curvature is reflected along its own path
A ray of light travelling to the mirror through the principal focus is reflected parallel to the principal axis
Note: Any two of these rays are sufficient to locate the image.
Procedure to draw ray diagrams o Choose an appropriate scale so that the ray diagram fits on the available space. o Draw a horizontal line to represent the principal axis of the mirror. Mark the focal point of the mirror.
Using the chosen scale, draw the object in position along the principal axis. The object is drawn as a vertical line from the principal axis.
Locate the position of the image by drawing rays from the object to the mirror. Use the rules for drawing ray diagrams to draw the reflected rays.
At the point of intersection of the reflected rays, draw the image in position
Image formed in Curved mirror
Terms used to describe the images formed by curved mirrors:
Real image is on the same side of the mirror as the object.
Virtual image is on the opposite side of the mirror compared to the object.
Upright image has the same orientation as the object.
Inverted image is oriented in an upside down position compared to the object.
Enlarged image is bigger than the object.
Diminished image is smaller than the object
Images formed by Concave mirrors
The following are the characteristics of images formed by concave mirrors:
An object 5 cm tall is placed 34 cm from a concave mirror of focal length 20 cm. By means of an accurate graphical construction, determine the position, size and the nature of the image formed.