# IFS (Forests Services) Physics (Mains): Questions 16 - 20 of 34

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## Question number: 16

» Special Relativity, Waves & Geometrical Optics » Geometrical Optics » System of Two Thin Lenses

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Appeared in Year: 2010

Essay Question▾

### Describe in Detail

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,

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## Question number: 17

» Classical Mechanics » System of Particles » Constraints

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Appeared in Year: 2010

Essay Question▾

### Describe in Detail

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 coordin

… (305 more words) …

## Question number: 18

» Physical Optics » Polarisation and Modern Optics » Principles of Fibre Optics Attenuation

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Appeared in Year: 2010

Essay Question▾

### Describe in Detail

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

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## Question number: 19

» Physical Optics » Polarisation and Modern Optics » Principles of Fibre Optics Attenuation

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Appeared in Year: 2010

### Write in Short

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

## Question number: 20

» Physical Optics » Polarisation and Modern Optics » Single Mode Fibres

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Appeared in Year: 2010