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### Course: MCAT>Unit 9

Lesson 20: Spherical mirrors

# Convex parabolic mirrors

Convex Parabolic Mirrors. Created by Sal Khan.

## Want to join the conversation?

• Is there just ONE case for the image to be formed in a convex mirror?
• You will always get small virtual image between the focal point and vertex of the mirror. In case object is at infinity, image is formed behind the mirror at focal point like a point.
• If you make a bunch of micro holes in the surface of the convex mirror facing the object, and you put a screen on the other side, behind the surface, do you get a real image?
• No, you won't, because virtual images aren't formed in physical space. If you make a bunch of holes in, say, your bathroom mirror, all you would see is your reflection riddled with holes through which you'd see the wooden frame or whatever. Same thing goes for convex mirrors. The non-mirror spaces left by the holes would just reflect light diffusely.
• So convex mirrors can't form images beyond the focal point?
• The object from infinity, in case of convex mirrors, will appear to form an image at Focus (of course). Then what will be the nature of the image. Will it be virtual and erect? highly diminished?
• in case of convex mirrors the rays bend outwards an dhence do not meet but when we extend them backwards (imaginary concept) they appear to meet forming a virtual erect and highly diminished image
• so is the convex mirrors are always form smaller and upright virtual image ?
(1 vote)
• Yes. Since they are diverging mirrors, they'll form virtual image for real object.(They'll produce real images for virtual objects though).

And since,
``1/v=1/f-1/u``

=>f is positive, u is negative, So, 1/v is greater than 1/u. So, v is lesser than u and v is positive,

=>Magnification=m=-v/u=> Positive but less than 1.=>Smaller image.
• what does the center of curvature mean ???what does it do???
• the radius of spherical mirror of which the reflecting surface of a spherical mirror forms a part is called the center of curvature.
It is denoted by the letter "R"
(1 vote)
• Why is the focus at the opposite side?
(1 vote)
• The focus is the point in space where the lines described by the reflected rays cross. With a convex mirror the actual path of the incoming light rays diverge and will never cross in front of the mirror so the focus is behind the mirror. This is similar to a concave lens.
• I've just heard that the focal length of a plane mirror is infinite. I don't get it. How is that so?
(1 vote)
• The focal length is determined by where the rays from the mirror intersect. The rays from a flat mirror never intersect, right?
• At Why does the light reflect in a way that looks like it's coming from the focus? Why doesn't it reflect in a way that looks like how it would reflect if the mirror was straight, you know like when you set up a normal line and the angle of incidence is equal to the angle of reflection?