Mirrors and Lenses

Science, Grade 6

1. Mirrors and Lenses
What happens to the image’s size and placement as an object is moved closer to a mirror or lens? Is there a relationship between an object and its image? In this virtual investigation you will choose a type of mirror or lens and investigate the properties of the image formed. When the object in front of the lens or mirror is moved, the size and placement of the image will be displayed. The following variables are used to represent distances and heights: is the distance from object to mirror/lens, is the distance from the image to the mirror/lens, is the height of the object, and is the height of the image.All parallel light rays that strike a mirror converge to one point called the focal point. The distance from the mirror to this point is called the focal length. The focal length depends on the shape of the mirror. In optics not all distances are represented by positive numbers. The focal length of a convex mirror is a negative distance. This negative distance actually represents a point on the “wrong side”, in back, of the mirror. An image can also be on this “wrong side”. For any mirror, if an image distance is negative, then the image is located behind the mirror. Lenses have the same properties. A concave lens also has a negative focal length. For any lens, if an image distance is negative, the image is located in front of the lens.Don’t forget the following information when deciding if an image is real or virtual.All real images are upside down. Real images are in front of the mirror or on the far side of a lens.All virtual images are upright. Virtual images are behind the mirror or in front of the lens.