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LECTURE 4 : January 29,2021
CLASS : XII
CHAPTER : 09, RAY OPTICS
PRESENTED BY : MANOJ SHARMA
LECTURER, RPVV
SEC 10 DWARKA
TEAM PHYSICS
Mr. MANOJ Dr. ARVIND Ms. SARITA SAXENA Mr. PRABHA KANT
SHARMA KUMAR RPVV IP Extn. SHARMA
RPVV Sec-10 (Coordinator) RPVV Kishan Ganj
Dwarka. Core Academic
Unit
Mr. GAUTAM P. NAUTIYAL Mr. AKASH, School of Mr. YASHVIR SINGH Mr. JOGINDER
School of Excellence, Excellence RPVV Rohini sec 11
Anti pollution campaign in the national
capital
The campaign is started
from October 21,2020.
nearly 15-20% vehicular
pollution can be
controlled
References
▪ The content for this presentation has been
taken from NCERT and INTERNET.
▪ The purpose of this presentation is purely
educational.
We acknowledge and thank all holders for
their right.
Recap(Lecture 3)
▪ Refraction through a prism
▪ Angle of deviation
▪ Prism formula
▪ Simple microscope
Topics to be covered
• Compound microscope
• Astronomical telescope(refracting type)
• Astronomical telescope(reflecting type)
• Advantages of reflecting type telescope
CH: 9 (lecture:4)
Compound microscope
A simple microscope has a limitation. We can not achieve angular
magnification more than 9 using simple microscope for realistic focal
lengths.
For much larger magnifications, one uses two lenses, one
compounding the effect of the other. This is known as a compound
microscope.
Construction
A compound microscope consists of two lenses:
1.Objective : The lens near the object, called the objective.It is a
convex lens of small aperture and small focal length
f o.
2.Eyepiece : The lens where we keep our eye to see final image.It is a
convex lens of moderate aperture and small focal
length fe such that ( f e > fo )
Ray Diagram
Working
• The object (AB) is placed beyond the focus of objective which forms a real
image (A’B’).
• This serves as the object for the second lens, the eyepiece, which functions
essentially like a simple microscope or magnifier, produces the final image
(A”B”), which is enlarged and virtual.
• The final image formed by the eyepiece can be viewed at near point for
maximum magnification (near point vision) or at infinity for relaxed eye.
Magnifying Power
Magnifying Power : The ratio of angle subtended by image to the angle
subtended by object at eye when both are placed at near point. This is also
called Angular magnification.
Magnifying Power
Magnifying Power
Magnifying Power
Numerical Problem
The total magnification produced by a compound microscope is 20.The magnification
produced by the eyepiece is 5.The microscope is focussed on a certain object.The
distance between the objective and eyepiece is observed to be 14cm.If the least
distance of distinct vision is 20cm calculate the focal length of the objective and the
eyepiece.
Numerical Problem
The total magnification produced by a compound microscope is 20.The magnification
produced by the eyepiece is 5.The microscope is focussed on a certain object.The
distance between the objective and eyepiece is observed to be 14cm.If the least
distance of distinct vision is 20cm calculate the focal length of the objective and the
eyepiece.
Solution:
Astronomical Telescope
A telescope is used to provide angular magnification of distant objects.
An astronomical telescope is used to see celestial objects like stars
and planets. It consists of two lenses-
Objective : It is a convex lens of large aperture and large focal length fo.
Eyepiece : It is a convex lens of small aperture and small focal length fe.
Working : Light from a distant object enters the objective and a real
image is formed in the tube at its second focal point. The eyepiece
magnifies this image producing a final inverted image
Ray Diagram
Normal adjustment : When final image is formed at infinity.
Angular magnification
Angular magnification
Angular magnification
Near point vision
Angular magnification
Angular magnification
NCERT Q.NO.9.34
NCERT Q.NO.9.35
a) For the telescope described in Exercise 9.34 (a), what is the separation
between the objective lens and the eyepiece?
b) If this telescope is used to view a 100 m tall tower 3 km away, what is the
height of the image of the tower formed by the objective lens?
c) What is the height of the final image of the tower if it is formed at 25cm?
Reflecting type telescope
Telescopes with mirror objectives are called reflecting telescopes.
It consists of a concave shaped parabolic mirror called objective and
an eyepiece to view the final image.
Reflecting type telescope
Advantages of reflecting type over refracting type.
❑ Images formed by reflecting type
are free from chromatic aberration.
❑ Images formed by reflecting type
are free from spherical aberration.
❑ Mechanical support is much less of
a problem since a mirror weighs much
less than a lens.
❑ Images formed by reflecting type telescope are more sharper and brighter.
For Today’s quiz and pdf notes :
Click on the links given in
description box.
