#engineering physics
- A diffraction grating used at normal incidence gives a line, λ1 = 6000 A˚ in a certain order superimposed Answer: about 2778 lines per cm. Grating equation: (e+d)sinθ = nλ . The n th order of λ₁ coincides with the (n+1) th order of λ₂ at the same... 1
- What is importance of resonant cavity in the operation of laser? Answer: the resonant (optical) cavity provides optical feedback: its mirrors send photons back and forth through the active medium so that s... 1
- How is multipath dispersion overcome in Graded index fibre? Answer: in a graded-index fibre the refractive index decreases from the axis outwards, so rays that travel longer paths away from the axis a... 1
- Distinguish between single mode and multimode optical fiber Answer: a single-mode fibre has a very thin core that allows only one path (mode) of light; a multimode fibre has a wider core that allows m... 1
- Distinguish between step index and graded index optical fiber. Answer: in a step-index fibre the core has a uniform refractive index that drops suddenly at the cladding; in a graded-index fibre the core... 1
- Derive Maxwell’s third equation in integral and differential form. Given that D = 20x î +10 ĵ (C/m2 ).
- Draw the schematic diagram of Scanning Electron Microscope and explain its construction, working, advantages
- What is population inversion state? Explain its significance in the operation of LASER. Answer: population inversion is the state in which more atoms are in a higher (excited) energy level than in a lower energy level. It is ess... 1
- Compute the maximum radius allowed for a fiber having core refractive index 1.5 and 1.48. Answer: maximum core radius ≈ 2.35\ μm (core diameter about 4.7 µm). A step-index fibre supports only one mode if its normalised frequency (... 1
- What is a grating? Define grating element? Discuss the phenomenon of Fraunhofer’s diffraction at a grating and obtain Answer: a grating is a large number of equal, equidistant parallel slits; the grating element is (e+d) , the width of one slit plus one opaq... 1
- Discuss the phenomenon of Fraunhofer’s diffraction at a single slit and obtain the condition for the first minimum. Answer: in Fraunhofer single-slit diffraction the first minimum occurs where asinθ = λ . For the grating, the maximum order visible is 14. P... 1
- With neat energy level diagram describe the construction and working of a He-Ne Laser.
- What are different techniques to synthesize nanomaterials? Explain any one of them in detail. Answer: nanomaterials are synthesised by top-down methods (ball milling, lithography, etching, laser ablation) or bottom-up methods (sol-gel... 1
- State the advantages of optical fiber cables on conventional electrical cables Answer: optical fibres carry far more information over longer distances with lower loss, are immune to electrical interference, and are ligh... 1
- Find the divergence and curl of a vector A= x2 y î + (x-y) k ̂ Answer: nabla·vec A = 2xy and nabla×vec A = -hat i - hat j - x²hat k . Here A_x = x²y , A_y = 0 , A_z = x - y . Divergence nabla·vec A = ∂ A... 1
- Derive the expression of numerical aperture for a step index fiber. A light ray enters an optical fiber from air. Answer: NA = sqrtn₁²-n₂² . For the given fibre, critical angle ≈ 68.1^° and NA ≈ 0.568 . Derivation Let the core index be n₁ , cladding inde... 1
- Light is incident normally on a grating 0.25 cm wide with 1250 lines. Data : Number of lines / cm (N)= 5000 m=1 λ1=5895 Å λ2=5901 Å Formula : (a+b)sinθ=Nλ mN=λ/dλ Calculations : ---1 ----2 ---3 Number of lines... 2
- Explain top down and bottom up approaches to prepare nanomaterials. Answer: in the top-down approach a bulk material is broken down into nanosized pieces; in the bottom-up approach nanostructures are built up... 1
- Explain the construction and reconstruction of hologram. Answer: a hologram is made by recording, on a photographic plate, the interference pattern between laser light scattered from an object (obj... 1
- How many orders will be observed by grating having 4000 lines/cm, if it is illuminated by light of wavelength Grating equation is (a+b) sinθ =nλ , N= 4000 lines/cm For maximum orders sinθ = 1 Therefore , n_max = (a+b)/λ = 1/Nλ For 5000 Å, n_max = fra... 2
- How many orders will be observed by grating having 4000 lines per cm,if it is illuminated by light of wavelength order is 3-5 2
- A light of wavelength 6500 A0 falls normally on a grating surface. The first order spectrum is obtained grating element is 1.947*10⁻⁴cm 1
- Calculate the highest order spectrum that can be obtained by a monochromatic light of wavelength 6000A0 by a grating Highest order is 2 1
- Diffraction pattern of single slit of width 0.5 cm is formed by lens of focal length 30 cm . distance between the first dark & the next bright fringe from the axis is 0.0036 cm 2