Page 54 - Physics 10_Float

GEOMETRICAL OPTICS

12.11 APPLICATIONS OF LENSES
Now we discuss applications of lenses in some optical devices
such as camera, slide projector and photograph enlarger.
1. CAMERA
A simple camera consists of a light-proof box with a
converging lens in front and a light sensitive plate or film at
the back. The lens focuses images to be photographed onto
the film. In simple lens camera, the distance between lens
and film is fixed which is equal to the focal length of the lens.
In camera, object is placed beyond 2F. A real, inverted and
diminished image is formed in this way as shown in Fig.12.27.

Convex lens
Object to be
photographed Film
Principal axis
Focal Real,
point inverted
image

Fig.12.27: Schematic diagram of camera

2. SLIDE PROJECTOR
Fig.12.28 shows how a slide or movie projector works. The
light source is placed at the centre of curvature of a
converging or concave mirror. The concave mirror is used to Self Assessment
reflect light back in fairly parallel rays. The condenser is made
Where a pen is placed in front
up of 2 converging lenses that refract the light so all parts of
of a convex lens if the image is
the slide are illuminated with parallel rays.
equal to the size of the pen?
Concave mirror Slide What will be the power of the
Light source lens in dioptres?
Screen

Condenser lenses Projection lens
Fig.12.28: Diagram of slide projector
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