# Question Bank Solutions for BE Electrical Engineering Semester 2 (FE First Year) - University of Mumbai - Applied Physics 2

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Applied Physics 2
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Calculate the V number of an optical fibre having numerical aperture 0.25 and core diameter 20 μm, if its operating wavelength is 1.55 μm.

 Fibre Optics
Chapter:  Fibre Optics
Concept: Total Internal Reflection

With neat ray diagram explain the concept of total internal reflection (TIR).

 Fibre Optics
Chapter:  Fibre Optics
Concept: Total Internal Reflection

Obtain the condition for maxima and minima of the light reflected from a thin transparent film of uniform thickness. Why is the visibility of the fringe much higher in the reflected system than in the transmitted system.

 Interference and Diffraction of Light
Chapter:  Interference and Diffraction of Light
Concept: Interference in Thin Film of Constant Thickness Due to Reflected and Transmitted Light

What is Numerical aperture? Explain the use of optical fibre in temperature sensor. The core diameter of a multimode step index fibre is 50 μm. The numerical aperture is 0.25. Calculate the number of guided modes at an operating wavelength of 0.75 μm.

 Fibre Optics
Chapter:  Fibre Optics
Concept: Numerical Aperture

Explain spherical co-ordinate system. State the transformation relation between Cartesian and spherical co-ordinates.

 Electrodynamics
Chapter:  Electrodynamics
Concept: Cylindrical and Spherical Coordinate System

an electron is accelerated through a potential difference of 5kv and enters a uniform magnetic field of 0.02 wb/m2 acting normal to the direction of electron motion. Determine radius of the path.

 Charge Particle in Electric and Magnetic Fields
Chapter:  Charge Particle in Electric and Magnetic Fields
Concept: Motion of Electron in Electric Field

The core diameter of multimode step index fibre is 50 μm.The numerical aperture is 0.25. Calculate the number of guided modes at an operating wavelength of 0.75 μm.

 Fibre Optics
Chapter:  Fibre Optics
Concept: Numerical Aperture

What is meant by thin film? Comment on the colours in thin film in sunlight.

 Interference and Diffraction of Light
Chapter:  Interference and Diffraction of Light
Concept: Interference in Thin Film of Constant Thickness Due to Reflected and Transmitted Light

Derive the conditions of maxima and minima due to interference of light transmitted from thin film of uniform thickness.

 Interference and Diffraction of Light
Chapter:  Interference and Diffraction of Light
Concept: Interference in Thin Film of Constant Thickness Due to Reflected and Transmitted Light

Difference between step index and graded index fibre.
An optical fibre has a numerical aperture of 0.20 and refractive index of cladding is 1.59. Determine the core refractive index and the acceptance angle for the fibre in water which has a refractive index of 1.33.

 Fibre Optics
Chapter:  Fibre Optics
Concept: Numerical Aperture

Explain cylindrical co-ordinate system.
State the transformation relation between cartesian and cylindrical co-ordinates.

 Electrodynamics
Chapter:  Electrodynamics
Concept: Cylindrical and Spherical Coordinate System

Using spherical co-ordinate systems calculate the area of a disc of radius 2 cm.

 Electrodynamics
Chapter:  Electrodynamics
Concept: Cylindrical and Spherical Coordinate System

Differentiate between spontaneous and stimulated emission.

 Lasers
Chapter:  Lasers
Concept: Spontaneous Emission and Stimulated Emission

Find cylindrical co-ordinates of a point (3𝒊̅ + 4𝒋̅ + 𝒌̅)

 Electrodynamics
Chapter:  Electrodynamics
Concept: Cylindrical and Spherical Coordinate System

Derive the conditions of maxima and minima due to interference of light reflected from thin film of uniform thickness.

 Interference and Diffraction of Light
Chapter:  Interference and Diffraction of Light
Concept: Interference in Thin Film of Constant Thickness Due to Reflected and Transmitted Light

Derive the formula for numerical aperture of step index fibre and give it’s physical significance.The N.A of of an optical fibre is 0.5 and the core refractive index is 1.54.Find the refractive index of cladding.

 Fibre Optics
Chapter:  Fibre Optics
Concept: Numerical Aperture

Derive the formula for numerical aperture of step index fibre and give it’s physical significance.The N.A of of an optical fibre is 0.5 and the core refractive index is 1.54.Find the refractive index of cladding.

 Fibre Optics
Chapter:  Fibre Optics
Concept: Numerical Aperture

What is antireflection coating? What should be the refractive index and minimum thickness of the coating?

 Interference and Diffraction of Light
Chapter:  Interference and Diffraction of Light
Concept: Interference in Thin Film of Constant Thickness Due to Reflected and Transmitted Light

A glass material A with an optical fibre is made has a refractive index of 1.55. This material is clad with another material whose refractive index is 1.51. The light in the fibre is launched from air. Calculate the numerical aperture of the fibre.

 Fibre Optics
Chapter:  Fibre Optics
Concept: Numerical Aperture

An electron enters a uniform magnetic field B=0.23x10-2 Wb/m2 at 450 angle to B. Determine the radius and pitch of helical path. Assume electron speed to be 3x107 m/s.

 Charge Particle in Electric and Magnetic Fields
Chapter:  Charge Particle in Electric and Magnetic Fields
Concept: Motion of Electron in Electric Field
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