Optionals IAS Mains Physics: Questions 16 - 20 of 306

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Question 16

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Appeared in Year: 2010

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Essay▾

Consider a system of two thin lenses of focal lengths and separated by a distance of in air. For an object of height placed at a distance of in front of the convex lens, find the size and position of the image. (Section A)

Explanation

  • Image from first lens is given as,
  • Now, the distance between lenses is , therefore for second lens image of first lens becomes object of second lens;
  • So, for second lens,
  • The image of object is at far from the second lens.
  • Now, magnification of lens is,
  • Since height of object is , therefore height of final image is .

Question 17

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Appeared in Year: 2010

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Essay▾

How can one introduce the constraints of motion through the concept of generalized coordinate systems? Write down the set of transformation equations for a system of particles relating the generalized coordinates with real coordinates. (Section A)

Explanation

  • In mechanics, mostly problems can be reduced by solving differential equation, which consist of all the forces acting on a system. A such equation is given by,
  • As we know, all mechanical systems have constraint force acting on them to some degree. A constrain in which the equations connecting the coordinates of the particles are called Holonomic co

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Question 18

Principles of Fibre Optics Attenuation
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Appeared in Year: 2010

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Essay▾

With a suitable diagram, deduce an expression for numerical aperture (NA) for ab optical fiber having refractive indices of core and cladding and , respectively and being placed in a medium of index . (Section – A)

Explanation

A Light Incident in Fiber

  • As shown in figure an optical fiber having refractive indices of core and cladding and , respectively. And is the refractive index of outside medium. A light beam incident at angle with core axis, and then it refracted at an angle and fall on the core – cladding interface at angle . Where,
  • From Snell’s Law, at point of

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Question 19

Principles of Fibre Optics Attenuation
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Appeared in Year: 2010

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Short Answer▾

Between multimode and single mode fibers, explain critically how and why single mode fiber is chosen for communication. (Section – A)

Question 20

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Appeared in Year: 2010

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Short Answer▾

Why are the two wavelengths and important in single – mode fiber – optical communication system? (Section – A)