Use Coupon: CART20 and get 20% off on all online Study Material

Total Price: R

There are no items in this cart.
Continue Shopping
Get instant 20% OFF on Online Material.
coupon code: MOB20 | View Course list

  • Kinematics & Rotational Motion
  • View Details
Get extra R 150 off



7 years ago


Answers : (1)


In focusing an image, a lens passes only the light that falls within its circular perimeter. From this point of view, a lens behaves like a circular aperture in an opaque screen. Such an aperture forms a diffraction pattern analogous to that of a single slit. Diffraction effects often limit the ability of telescopes and other optical instruments to form precise images.


The image formed by a lens can be distorted by other effects, including chromatic and spherical aberrations. These effects can be substantially reduced or eliminated by suitable shaping of the lens surfaces or by introducing correcting elements into the optical system. However, no amount of clever design can eliminate the effects of diffraction, which are determined only by the size of the aperture (the diameter of the lens) and the wavelength of the light. In diffraction, nature imposes a fundamental limitation on the precision of our instruments.


When we used geometrical optics to analyze lenses, we assumed diffraction not to occur. However, geometrical optics is itself an approximation, being the limit of wave optics. If we were to make a rigorous wave-optical analysis of the formation of an image by a lens, we would find that diffraction effects arise in a natural way.

Figure 42-13 shows the image of a distant point source of light (a star) formed on photographic film placed in the focal plane of the converging lens of a telescope. It is not a point, as the (approximate) geometrical optics treatment suggests, but a circular disk surrounded by several progressively fainter secondary rings. Comparison with Figure 42-1 leaves little doubt that we are dealing with a diffraction by a circular aperture, which is beyond the level of this text, shows that (under Fraunhofer conditions) the first minimum occurs at an angle from the central axis given by


sin q = 1.22 λ/d


where d is the diameter of the aperture. This is to be compared with Equation



sin q =



which locates the first minimum of a sit of width a. These expressions differ by the factor 1.22, which arises when we divide the circular aperture into elementary Huygens sources and integrate over the aperture.


7 years ago

Post Your Answer

Other Related Questions on General Physics

For a body moving in circular motion with a constant angular velocity, the magnitude of average acceleration over a period of half a revolution is x times th emagnitude of its instantaneous ...
Average accln. = (vjcap – (-vjcap))/(pi/w) = > 2vjcap*w/pi where w is constant angular velocity given. Now, Given 2v*w/pi = x * dv/dt dv/v = (2*w/x*pi)dt integerate both sides logv =...
Vikas TU one month ago
three dogs sitting at the vertices of an equilateral triangle. The length of each side of the triangle equals to s meters. A person gives the command "Start!" and each dog starts to run...
In this type of question you can just find the velocity at which the separation b/w them is reduced,that is the net contribution of of all the velocities along the line joining both the...
Piyush Behera 5 days ago
Speed is vcos60 now we have distance =d and speed equal vcos60 so time is t=d/vcos60 that is 2d/v . Tell me if answer is wrong
Tushar 10 days ago
In a above question let us assume on sog at rest now component of first dog along o ther dog(assumed to be at rest ) so
Tushar 10 days ago
A bar magnet is placed in north - south direction with its north pole towards north . In which direction from the centre of the magnetic field will the points of zero magnetic field lie (a) ...
it has been kept in that way and not suspended freely . read the question before you reply. A bar magnet is placed in north - south direction with its north pole towards north . In which...
soumya 2 months ago
From the Earth’s point of view, the North pole of the bar magnet would be at geographically south andthe South pole of the magnet would be at geographically North. This is the fact. as...
Vikas TU 2 months ago
What is kirchoffs current rule?explain it your own words???????????
The term Node in an electrical circuit generally refers to a connection or junction of two or more current carrying paths or elements such as cables and components. Also for current to flow ...
sudarshan 9 months ago
kirchhoffs law: two laws concerning electric networks in which steady currents are flowing. The first law states that the algebraic sum of the currents in all the conductors that meet in a...
T.kumar 9 months ago
Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were...
raj 9 months ago
Question is based on cross product. it is attached.
no the question is how do we know, for example calculate torque. F=2i+3j and r=4i. so is it F cross r or r cross F and how do we decide which is correct. According to the question they used ...
Naveen Shankar one month ago
while writing in vector form you will see it has FsSin@ (where @=theta angle). so while using i vector or j vector or k vector the whole sign changes so -that is the significance of writing ...
dipika kumari Sahoo one month ago
Torque is always r x F and never F x r . If the answer in your book is given for F x r then it is wrong. The example u gave torque should be -12k
Manas Shukla one month ago
Date of JEE advanced exam 2016? any idea????????????????????
Its on 22 nd May
Harsh Patodia 8 months ago
View all Questions »

  • Complete JEE Main/Advanced Course and Test Series
  • OFFERED PRICE: R 15,000
  • View Details
Get extra R 3,750 off

  • Kinematics & Rotational Motion
  • View Details

Get extra R 150 off

More Questions On General Physics

Ask Experts

Have any Question? Ask Experts

Post Question

Answer ‘n’ Earn
Attractive Gift
To Win!!!
Click Here for details