Concave mirrors are used in a wide variety of applications, including flashlights, telescopes, microscopes, car headlights, solar cookers, satellite dishes, and makeup or shaving mirrors. Theoretically, these mirrors can be thought of as part of an incomplete sphere, and a line can be drawn dividing that sphere in half. The midpoint of that line is known as the center, the point where that line intersects the mirror is the vertex, and the midpoint between the center and vertex is known as the focal point. The location of an object relative to the center of a concave mirror is extremely important in shaping the formed image. Objects located outside the center of the mirror, at the center of the mirror and inside the mirror's center all form distinct images with different characteristics.
Object Located Outside the Center of a Concave Mirror
The image formed when an object is located outside the center of a concave mirror will be real, which simply means that light rays actually pass through the image. This differs from the virtual images formed by plane mirrors which only appear to have light rays pass through them. The image formed by an object located outside the center of a concave mirror will also be vertically inverted and smaller than the real object.
Object Located at the Center of a Concave Mirror
The image formed when an object is located at the center of a concave mirror will again be real and vertically inverted, but in this scenario, the image will be equivalent in size to the object.
Object Located Between the Center and Focal Point of a Concave Mirror
The image formed when an object is located between the center and focal point of a concave mirror is once again real and vertically inverted. However, the formed image is now larger in size when compared to the object.
Object Located at the Focal Point of a Concave Mirror
No image is formed when an object is located at the focal point of a concave mirror. The reason for this interesting phenomenon is that the rays reflected from the mirror actually travel parallel to one another. Thus, the rays never converge to form an image.
Object Located Between the Focal Point and Vertex of a Concave Mirror
The image formed when an object is located between the focal point and vertex of a concave mirror is virtual. This occurs because the light rays that hit the surface of the concave mirror diverge upon reflection. The image formed actually occurs behind the mirror. Thus, even though light rays appear to be emanating from the image, no light rays pass behind the mirror. Also, when the object is located between the focal point and vertex of a concave mirror, the image formed will be upright and magnified.
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