Final Answer:
In ray tracing to find the image of a lens, typically three special rays are used: the parallel ray, the focal ray, and the central ray.
Step-by-step explanation:
Ray tracing involves using specific rays to determine the location and properties of an image formed by a lens. The first special ray is the parallel ray (r), which travels parallel to the lens axis before refraction, passing through the focal point on the opposite side after refraction. The second ray, the focal ray (r'), originates from the object and travels through the focal point before being refracted parallel to the lens axis. Lastly, the central ray (_r_0) passes through the center of the lens and continues in a straight line without deviation. These three rays are fundamental in determining the formation of the image.
The parallel ray (r) is used to ascertain the refracted ray's direction when coming from infinity. According to the lens formula,
where f represents the focal length, v is the image distance, and u is the object distance. For the focal ray (r'), its path is reversed compared to the parallel ray, following the same lens formula principles. Lastly, the central ray (_r_0) remains undeflected as it passes through the center of the lens.
By analyzing these three special rays, we can determine the characteristics of the image formed by the lens, such as its size, orientation, and whether it is real or virtual. Understanding these rays helps in visualizing the image formation process and comprehending the principles governing the behavior of light passing through lenses.