# Physical Optics-Polarisation and Modern Optics (IFS (Forests Services) Physics (Mains)): Questions 1 - 5 of 5

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## Question number: 1

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

Appeared in Year: 2012

Essay Question▾

### Describe in Detail

A step – index silica fiber consists of core of refractive index 1.450 and diameter . If the numerical aperture of the fiber is 0.16, calculate:

(i) the acceptance angle of the fiber,

(ii) refractive index of the cladding, and

(iii) if the fiber is immersed in water of refractive index 1.33, how does the acceptance angle change? (paper -1) (Section – A)

### Explanation

• Here, from question, we can say,

• The numerical aperture of the optical fiber is given as,

• where, is acceptance angle of the fiber. is the refracting medium of surrounding of optical fiber. And are the refracting indexes of core and cladding of the
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## Question number: 2

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

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

a Light Incident in Fiber

In figure a light beam is incident in core of optical fiber is shown.

• 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

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## Question number: 3

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

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: 4

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

Appeared in Year: 2010

### Write in Short

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

## Question number: 5

» Physical Optics » Polarisation and Modern Optics » Ruby and He-Ne Lasers

Appeared in Year: 2013

Essay Question▾

### Describe in Detail

Explain the lasing action of laser using energy level diagram and describe the operation of laser experimental setup. (Section A)

### Explanation

• The light is produced in He – Ne laser by atomic transitions in the Neon atom. The Helium acts as a buffer gas in it. That means Helium doesn’t directly produce laser light, it only helps the atom of the Neon gas to produce lasing in as manner.

• Helium absorbed

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