in the torch reflector cancave mirror is used then why convex mirror are used as reflector in street lamps

In a torch the bulb is placed at the focal point of the concave mirror so that the light from the bulb is reflected as a parallel or nearly parallel beam. This helps the user to see specifically what he wants to see with the help of the torch.

A street lamp uses a convex mirror so that the light from the bulb is spread as wide as possible. This allows the light to spread all over the street.

 

 

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Convex mirror is also called diverging mirror as it diverges the beam of light falling on it. It ia for this purpose that it is used in street lamps as it would diverge the light rays and hence spread the light so that visibility increases.

On the other hand concave mirror is also called converging mirror. It is used for different light rays falling on it to a single point. Now we use search light and torches so that we have a more focused light beam which will not diverge out and hence help in searching. Due to this reason we use concave mirror in torches and search lights.

Case 2

As stated above concave mirrors help to produce more focused beam of light . due to this reason , it is used in reflecting type telescopes. It has large aperture . It is free from chromatic and spherical aberrations . The image formed is much brighter as a result. Also the resolving power of this telescope is much greater than the refracting type telescope. hence the statement is wrong that convex mirrors are used in reflecting type telescope. For further explanation just view the following diagram :

Here as we can see that the primary mirror is the concave mirror with large aperture. It produces inverted image but we know that most of the astronomical bodies are spherical hence it doesn't matter.

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