Page 174 - Science Class 08
P. 174
op cal device is used to view small things in a microscopes are used by scien sts to observe
short-range a er enlarging their images so that ny cells of living bodies.
they may be seen quite clearly. It has lenses Op cal Telescope
that deflect light-rays such that the object can
The word ‘telescope’ is made up of two parts
be observed quite clearly. This device was
tele + scope = distant + range. Clearly, this op cal
invented by Anton van Leeuwen-hoek in.
device is used to view distant things that cannot
Construc on : The microscope has three parts seen with the naked eye easily. Very strong
— the foot, body and the tube. The foot forms telescopes called astronomical telescopes are
the base on which the device stands. The body used to observe heavenly bodies.
does the job of holding the tube erect. It is
Construc on : A telescope consists of a long
hinged to mirror at its lower end. As for the
heavy tube. At its viewing end is a small eye-
tube, it has two lenses — one at its upper end
piece with two lenses so that the distant object
and the other at its lower end.
may appear quite larger. At its other end is a
Eyepiece larger lens called the objec ve lens that
gathers light reflected by the object to be
observed. The telescope can be focussed by
Head adjus ng the distance between the eyepiece
Arm
Objec ve Lens and the objec ve lens.
Coarse
Adjustment
Fine Telescope or Whitecard with a
Adjustment Binoculars magnified image of
Stage the sun
Base
Condenser
Mirror
Microscope
Cardboard
Working : The object to be seen is placed on Collar
the stage above the mirror which is adjusted so
that it may reflect light through an opening
onto the stage and let the object shine in it.
Then, the tube is adjusted by means of a
focussing knob such the lens called objec ve Working : When the light from the object to be
lens at its lower end deflects the light to make observed strikes at the objec ve lens, its rays
the object shine to be seen clearly. The object get deflected to converge at the focus where a
lying on the stage is, in fact, between the small inverted image of the object is formed
op cal centre of the lens and its focus. So, its between the focus and the eyepiece that
image is much larger and the observer can makes it larger enough to be seen as also it
seen it easily through the upper lens called looks much closer to the eye.
eyepiece. In order to make the image s ll large, Some telescopes have special lenses that show
another convex lens can be added. Such the inverted images in their erect posi ons.
174 Science-8
