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### Course: MCAT>Unit 9

Lesson 20: Spherical mirrors

# Parabolic mirrors 2

Parabolic Mirrors 2. Created by Sal Khan.

## Want to join the conversation?

• At does that mean that if you stood in front of a parabolic mirror in a fun house at the focus, you would see no image of yourself at all? I've never tried it, but it seems far-fetched.
• Theoretically, If it were a concave mirror, No, you cannot see yourself since the rays are parallel and they do not intersect. So, the image does not form.
Practically, there are other effects that affect the image formation, like spherical aberration, Chromatic aberration, reflection of the light through dust particles, not perfect mirror ...
• When the object is in front of the mirror you get a real image, now why I see the reflexion in the mirror? for instance in a spoon I see my reflexion inverted but not in front of the spoon I see it in the spoon, it looks like the image is virtual.
Than you.
• That's because the object (in this case, your face) is "after" the focus of the spoon. So as Sal explained in the last case, the image is fact virtual.
• Will we be able to see the real image without screen?
• Yes, but it is that if you are not at the point where they meet, then you may see a distorted image.
(1 vote)
• If an incident ray were to go through the center of curvature, would it's reflected ray go directly back along the same path it's incident ray took?
• yes, a ray that passes through the centre of curviture goes straight back along its path
• What exactly is the center of curvature?
• In calculus, we talk about curvature of a function. Imagine it as if you were driving along a road shaped like your function (in this case, a parabola). At a specific point, you ceased to turn the wheel and held it in the current position. You would begin to drive in a circle, right? The center of curvature IS the center of that circle!
• what if the object is at infinity?.....where will the image be formed then?
• If the object is at infinity, the object will be formed in the image focal plan (I don't know how to translate it from french)

Explanation :

You already know that a ray passing by O (the center of the lens) will forever go straight, and that a ray passing by F will be devied perpendicularly to the lens. You also know that before they hit the lens, the rays of an object at infinity will be parallel. So, the meeting point of these two rays will always be in the image focal plan : so F' and A' will be the same point.

I tried to do my best to translate, tell me if you don't understand ;)
• Can parabolic mirrors and magnifying glasses be used to make a highly concentrated beam of light ( a laser )
• It is impossible to form a narrowly confined completely parallel beam of light from a divergent bundle of light. You can focus it down to a point, but behind that point it will diverge nevertheless.

Apart from that, laser light has the property of being coherent, i.e. it consists of only one colour and has one defined phase (the pulsation of the electromagnetic field is very ordered). These properties are achievable only with a laser (or similar device).
• in the first few cases wouldn't you still be able to see your image in the concave mirror (virtual) but here if you trace back the lines they are diverging so how could u see an image in the mirror?