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When an object is placed in front of a concave mirror, a virtual image is created behind the mirror. The size of the virtual image depends on the distance the object is from the mirror. As the object gets closer to the mirror, the image gets smaller. However, when the object is far from the mirror, the image becomes larger and upright.
In order to create a virtual image, the light rays of the object must diverge, and meet at a point behind the mirror. This point is called the virtual image location. Once the rays diverge, they do not rejoin in the same path.
One way to find the virtual image location is to extend the reflected rays backwards beyond the mirror. You can then use a graphical method to draw the corresponding image locations. These are drawn in blue.
Another way to find the location is to look at the curve of the mirror. The radius of curvature is 30.0 cm. That's the magic number for the size of the image.
Erect image
Concave mirrors are used in flashlights, ophthalmoscopes, and astronomical telescopes. They produce an enlarged or virtual image of an object, depending on the location of the object in relation to the mirror.
To calculate the distance from an object to a concave mirror, you will need to know the focal length of the mirror. It is half of the radius of curvature of the mirror. This is measured from the mirror's pole. The focal length is also called the focal distance.
When an object is placed in the middle of the focus of a concave mirror, it will form an erect image. However, if the object is located outside the focus, it will form an inverted image.
