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5.5.5 Camera

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Functions

Convex lens To focus the light of an object onto the film so that a sharp image can be produced.
Diaphragm To control the size of the aperture and hence control the amount of light move into the camera.
Focusing Ring To adjust the distance between the lens and the film so that the image is sharply focus on the film.
Film
  1. Acts as a screen for the image to form onto it.
  2. Chemical on it will react when exposed to light and produce a photograph.
Shutter Open when picture is taken to allow light move onto the film.
The shutter speed is the length of time when the shutter is open. It control the amount of light move onto the film.
Aperture Open when picture is taken to allow light move onto the film.
The shutter speed is the length of time when the shutter is open. It control the amount of light move onto the film.

Note:

  1. The film, which is normally kept in total darkness, contains a light-sensitive chemical called silver bromide.
  2. When you press the camera button, a shutter in front of the film opens then shuts again, exposing the film to light for a brief moment only. 
  3. Different intensities and colours of light across the image cause varying chemical changes in the film, which can later be developed, 'fixed', and used in printing a photograph.
  4. The image formed on the film is
    1. Real
    2. Inverted
    3. Smaller than the object.

 

5.5.4 Compound Microscope

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Compound Microscope
Object lens Higher power
Eye lens Lower power
Position of the object The object is placed at a position between fo and 2fo.
Nature of the image, I1 Real, inverted and magnified
Position of the image, I1. The first image, I1 must be placed between the optical center of the eye lens with the eye lens principle focus point, fe.
Nature of the image, I2 Virtual, inverted and magnified
Distance in between the two lens The distance between the object lens and the eye lens in a compound microscope is bigger than the sum of the  focal length (fo + fe).
If the distance between both lenses are adjusted to less than (fo + fe), no image can be seen.
Magnification of the compound  microscope.

m1 = Linear magnification of the object lens
m2 = Linear magnification of the object lens

 

5.5.3 Astronomical Telescope

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Astronomical Telescope
Objective lens Lower power
Eye lens Higher power
Position of the object At infinity
Nature of the image, I1 Real, inverted and magnified
Position of the image, I1. At the principle focus of object lens, fo.
Nature of the image, I2 Virtual, inverted and smaller in size.
Distance in between the two lens
  1. The distance between the object lens and the eye lens in a compound microscope is equal to the sum of the  focal length (fo + fe).
  2. If the distance between both lenses are bigger than (fo + fe), no image can be seen.
Magnification of the compound  microscope.

 

 

5.5.2 Magnifying Glass

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  1. Magnifying glass is also known as simple microscope.
  2. A magnifying glass is a single convex lens with short focal length.
  3. The iage formed is
    1. virtual,
    2. magnified
    3. upright
  4. A magnifying glass enlarges the image of an object by increasing the virtual angle at the eye when the object is viewed.

 

5.4.7 Lens Formula

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The Lens Equation

  1. The following is the lens equation that relates the object distance (u), image distance (v) and the focal length.
  2. When using the lens equation to solve problem, it's important to note the positive negative sign of u, v and f.
  3. Table below give the conventional symbol and sign for u, v and f.
Positif
Negatif
u
Real object
Virtual object
v
Real image
Virtual image
f
Convex lens
Concave lens

 

 

5.4.6 Linear Magnification

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The linear magnification is a quantity that indicates the ratio of the height of the image to the height of the object.



m = linear magnification
u = distance of object
v = distance of image
hi = heigth of image
ho = heigth of object

 

5.4.4 Images Formed by Thin Convex Lens

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Characteristics of the Image Formed by a Convex Lens

  1. As with a curved mirror, the position and size of an image can be found by drawing a ray diagram.
  2. Any two of the following three rays are sufficient to fix the position and size of the image.
  3. The characteristics, position and size of the image formed by a convex lens depends on the object distance (u) relative to the focal length (f)

Position of Object: u > 2f


Characteristics of the Image: Real, inverted, diminish
Distance of image: v < 2f

Position of Object: u = 2f


Characteristics of the Image: Real, inverted, same size
Distance of image: v = 2f

Position of Object: f < u < 2f


Characteristics of the Image: Real, inverted, magnified
Distance of image: v > 2f

Position of Object: u = f


Characteristics of the Image: -
Distance of image: At infinity

Position of Object: u < 2

Characteristics of the Image: Virtual, uprigh, magnified
Position of image: at the same side of the object

 

5.4.3 Ray Diagram for Lenses

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Rules for Drawing Ray Diagram for Convex Lenses

  1. A light ray passes through the optical centre of the lens will not be refracted.
  2. A light ray parallel to the principle axis of the lens will be refracted passes through the principle focus.
  3. A light ray passes through principle focus will be refracted parallel to the principle axis.

Rules in Drawing Ray Diagram for Concave Lens

  1. A light ray passes through the optical centre of the lens will not be refracted.
  2. A light ray parallel to the principle axis will be refracted away from the principle focus
  3. A light ray moving towards the optical centre will be refracted parallel to the principle axis.