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### Course: Class 10 Physics (India)>Unit 1

Lesson 2: Concave & convex mirrors and their applications

# Concave mirror applications

In this video, we will look at some applications of concave mirrors.  Created by Mahesh Shenoy.

## Want to join the conversation?

• what does focal length mean ?
• Focal length or 'f' is the length between the focus of the mirror and its pole.
Pole is a point which is on the mirror and is closest to the focus. It is the geometrical centre of the curve mirror surface.
• why am i getting bulgarian subtitles
• It is a default subtitle. You can go ahead and Auto-Translate to English if you require subtitles
• i have a question- that in the case of a torch as shown here i know that parallel rays of light are produced but when theyre passing through the glass which is there infront of the mirror for protection, then do those rays not undergo refraction? if so why do we not see them slanted??
• When the rays of light enter the glass, they will get refracted and will bend towards normal, because glass is a material that is denser than air. when they exit the glass, they will bend away from normal, because air is less denser than glass. Both these bendings will have the same value and will cancel out so the rays of light will still be parallel.

Lets say that when the rays enter the glass, they bend 17 degrees towards normal. when they exit the glass they will bend 17 degrees away from normal, and will still be parallel.

I hope this helped you understand the concept
(1 vote)
• I heard that images are formed at the point where reflected rays intersect...But the reflected rays not always intersect at the focus. Then?
• You are right, that the images are formed where the reflected or refracted rays intersect. However, this is not always the case. When the reflected rays do not intersect, it is assumed that the reflection of any object then forms at infinity, which is not visible to the human eye. This would be further elaborated in the Concave and Convex Mirrors and the concept of refraction
• for flashlight seems that the mirror is concave outward not inward?
(1 vote)
• When the light from the bulb hits the concave part of the flashlight, there will be rays which hit the surface parallelly. So there will be rays which end up converging as well. Would that result in the middle part of the light emitted by the flashlight to be brighter?
(1 vote)
• How does one determine where the focus of a concave or a concave reflector is?
I mean...how is the math done?
(1 vote)
• The Point of Focus, where all the reflected rays of light converge or meet, can be determined by either:
1. Ray Diagrams (elaborated in upcoming videos)
2. Focal Length formula (that shows where the focus point is): f=-r/2, where f=focal length and r=radius of the curvature of the mirror's surface
(1 vote)
• in the last application ( onwards), will the mirror used for reflecting sound be different from a normal mirror?
• Mirrors are not used for reflecting sound. These concave surfaces used for reflecting sound are called acoustic diffusers. They are usually used in big halls.
So..they are obviously different from normal mirrors
• why if the distance between torch and the opaque object is increased the circle of light also increase?
• This is what I understood. As Mahesh told us, the bulb is placed at the focus of the mirror and then the the rays which go backward and hit the mirror, DIVERGE from the torch (as can be seen in the video).
So, if the distance between torch and the object increases, definitely the circle of light will also increase.
• at he says the same thing twice
that the same angle to be incident ray even after interchanging