Transcript Image formation in a plane mirror.

What kind of light is emitted by regular (not self-luminous) objects?
Mirror as an image forming device…
Image – a pattern of light that provides visual representation of
reality…
Image - the optical counterpart of an object produced by an optical
device as a lens or mirror …
… a likeness of an object produced on a photographic material .
In optics we distinguish between real and virtual images.
Image formation in a plane mirror.
The image is always there, in a well defined position, whether you
look at it or not.
The image is formed behind the mirror at a distance equal to the
distance from the object, and has size equal to the size of the object.
It is a virtual image, since there is no light in the image location. The
light only appears to come from there.
How exactly do we see
(images of the) objects in a
mirror?
Pretty much the same way
as when we are looking at
the objects directly!
And there are always much
more rays emanating from
an object than getting to our
eyes.
That’s how different people
can see the same
object/image
In the overhead view of the figure below, the image of the
stone seen by observer 1 is at C. Where does observer 2
see the image – at A, at B, at C, at E, or not at all?
An image may be virtual or real, but in each case:
Position of an image is defined just as well as position of the
object!
It does not depend whether or from where you are looking at it!
Looking into a mirror at yourself:
For an unobstructed, complete view you
only need a mirror, which is a half of
your height.
Question:
What is going to happen to you image in the mirror if you walk
away from it?
Mirrors are known to turn left into
right, that is to make the image of
your left hand look as your right
hand.
Why don’t they turn objects
upside down?
Well, if you think about it, there are
many other things the mirrors do not
do….
But the question is still standing:
Why left to right and not upside down?
A short answer is it is because you usually hand a mirror on a wall. If you place
it on the floor and sand on it, you would actually see yourself upside down.
The mirrors actually do a very special transformation, known as
inversion, which cannot be reduced to translations and
rotations…
Maybe to turning inside out?...
Chiral objects and
chiral molecules…
Do you need a mirror to form an image?
Not necessarily. You can do reasonably
well with a flat refracting surface.
• The image formed by a flat refracting
surface is on the same side of the
surface as the object
– The image is virtual
– The image is formed between the
object and the surface
– The rays bend away from the normal
since n1 > n2
n1
n2
Examples of using of the ray approximation:
1) A point source, a screen, and a 1D and 2D apertures between
them.
What is the shape of the image on the screen? Image of what is it?
What does its size depend on?
The shape of the image
corresponds to the shape of the
object or of the aperture;
The image is an image of the
object (aperture);
Its size is proportional to the size
of the aperture and to the ratio of
distances
source to screen
source to aperture
Image by an aperture and sunlight:
It is always the image of the aperture corresponding to its profile.
It is formed everywhere in space past the aperture (an opening, a
window).
The image on a screen past an aperture is going to be relatively
sharp, wherever you put the screen, but it becomes less sharp as
the screen is moved furtehr away from the aperture. WHY?
Examples of using the ray approximation:
1) How do you get a point source? What does it mean, rays filling the
aperture? What happens if we close a half of the aperture?
2) Two point sources, an aperture and a screen. Want kind of pattern
on the screen do they produce? What about a line of point sources?
3) A line of point sources and a very small (pinhole) aperture. What
kind of image will be on the screen? What happens if we cover a half
of the aperture?
Image of the aperture
Image of the aperture.. mostly
Image of both the
aperture and the
source.
How do we get an image of the source?
Congratulations!
We have just discovered the earliest model of photo camera,
Camera obscura.
What are the drawbacks
of the camera obscura?
A pinhole does not let much
light through.
If you make the pinhole
larger, the sharpness is lost.
How do we improve a
pinhole?
Thin Lenses
A thin lens consists of a piece of glass or plastic, ground so that
each of its two refracting surfaces is a segment of either a sphere or
a plane…
A lens is thin when the radii of curvature are much bigger than its
thickness.
Lenses have two major applications: light collection and imaging
Diverging lenses are
Converging lenses are
thickest at the edges and
thickest in the middle and
have negative focal lengths
have positive focal lengths