Then the student sights at the image of the object pencil in the mirror. The object pencil is placed in front of a plane mirror. Two pencils are inserted into rubber stoppers one stoppered pencil serves as the object and the other serves to assist the student in locating the image. First, the method of parallax is used to locate the image of the object. In the process of determining the image location, the manner in which light from the object travels to your eye is investigated.
While simple, this concept of the line of sight is also profound! This very principle of the line of sight will assist us in understanding the formation of images in both this unit (reflection) and the next unit (refraction).Ī common Physics lab involves the determination of the image location of a pencil (or some object) as formed by a plane mirror. Regardless of the eye location, you will still need to sight along a line in a specific direction in order to view the object. If your eye were located at a different location, then you would see a different cone of rays. Although this light diverges from the object in a variety of directions, your eye only sees the very small diverging cone of rays that is coming towards it. It is a rather simple principle: In order to view an object, you must sight along a line at that object and when you do light will come from that object to your eye along the line of sight.Ī luminous object emits light in a variety of directions and an illuminated object reflects light in a variety of directions.
This directing of our sight in a specific direction is sometimes referred to as the line of sight. And if you wish to view the image of Mary in a mirror, then you must direct your sight along a line towards the location of Mary's image. If you wish to view Mary's feet, then you direct your sight along a line towards Mary's feet. If you wish to view the top of Mary's head, then you direct your sight along a line towards the top of her head. In the process of viewing Mary, you are directing your sight along a line in the direction of Mary. As you look at Mary in class, you are able to see Mary because she is illuminated with light and that light reflects off of her and travels to your eye. Whether it be a luminous object (that generates light of its own) or an illuminated object (that reflects the light that is incident upon it), you can only view the object when light from that object travels to your eye. When you reflect a point in the origin, both the x-coordinate and the y-coordinate are negated (their signs are changed).In the first section of Lesson 1, it was stated, "without light, there would be no sight." Everything that can be seen is seen only when light from that object travels to our eyes. Imagine a straight line connecting A to A' where the origin is the midpoint of the segment. Triangle A'B'C' is the image of triangle ABC after a point reflection in the origin. Assume that the origin is the point of reflection unless told otherwise. While any point in the coordinate plane may be used as a point of reflection, the most commonly used point is the origin.
Under a point reflection, figures do not change size or shape. For every point in the figure, there is another point found directly opposite it on the other side of the center such that the point of reflection becomes the midpoint of the segment joining the point with its image. By looking through the plastic, you can see what the reflection will look like on the other side and you can trace it with your pencil.Ī point reflection exists when a figure is built around a single point called the center of the figure, or point of reflection. The Mira is placed on the line of reflection and the original object is reflected in the plastic. You may be able to simply "count" these distances on the grid.Ī small plastic device, called a Mira ™, can be used when working with line reflections. Notice that each point of the original figure and its image are the same distance away from the line of reflection.
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