If you are given concave mirrors with focal length 10 cm, 15 cm and 20 cm, which one is most suitable for: 1) a shaving mirror 2) a dentist's mirror?

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The concave mirror with the shortest focal length (10 cm) is the most suitable for a dentist mirror, while the concave mirror with the longest focal length (20 cm) is the most suitable for a shaving mirror.

The concave mirror can produce various types of the images of objects, depending on...

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The concave mirror with the shortest focal length (10 cm) is the most suitable for a dentist mirror, while the concave mirror with the longest focal length (20 cm) is the most suitable for a shaving mirror.

The concave mirror can produce various types of the images of objects, depending on the distance between the object and the mirror. The images could be real or virtual, diminished or magnified, upright or inverted. For the purposes of dental work and shaving, it would be helpful if the image was magnified and upright. This happens if the object is placed between the focal point of the mirror and the mirror itself. Please see the reference link for a detailed description of how the type and location of the image depends on the distance between the object and the mirror.

Therefore, for dental work, the focal length of the mirror should be a few centimeters only, in order to be able to place the mirror so that the object (teeth) is in between the focal point and the mirror. However, it would be difficult to be that close to the mirror while shaving, so a longer focal length - such as 20 cm - would be more suitable. 

 

 

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