JNTU
JNTU B.Tech I ENGINEERING PHYSICS I Previous Question Paper (June - 2022 - R16)
Answer any five questions. All questions carry equal marks.
Main
Explain the theory of Newton’s rings. Derive an expression for the radius of the nth bright ring in Newton’s rings.
Answer
Newton's rings are formed by the interference of light waves reflected from the top and bottom surfaces of an air film of varying thickness between a plano-convex lens and a plane glass plate. When monochromatic light falls normally on the lens, the air film thickness increases from the point of contact outward, creating circular interference fringes.
For a point at distance r from the center, the air film thickness is t = r2 / 2R, where R is the radius of curvature of the lens. The condition for constructive interference (bright rings) is 2μt cos(r) = (2n + 1)λ / 2. For an air film (μ = 1) at normal incidence (cos(r) = 1), this becomes 2t = (2n + 1)λ / 2, where n = 0, 1, 2, ...
Substituting t = r2 / 2R:
This expression gives the radius of the nth bright ring.
Explain the Fraunhoffer diffraction due to single slit. Obtain the conditions for maxima and minima. In the diffraction grating, what is the effect of total number of lines and width of grating on the spectrum.
Answer
Fraunhofer diffraction occurs when both the light source and the screen are effectively at an infinite distance from a single slit of width 'a'. As wavefronts pass through the slit, secondary wavelets interfere to produce a diffraction pattern on the screen.
The condition for minima is given by a sin(θ) = nλ, where n = ±1, ±2, ... . The condition for secondary maxima is a sin(θ) = (2n + 1)λ / 2, where n = ±1, ±2, ... . The central maximum occurs at θ = 0.
In a diffraction grating, the resolving power is proportional to the total number of lines (N) and the order of the spectrum (m). Increasing the total number of lines (N) increases the sharpness of the spectral lines and the resolving power. The width of the grating (W = N * d) determines the angular dispersion; a larger width allows for a greater number of lines to contribute to the interference, resulting in higher resolution and a more distinct, widely separated spectrum.
Describe the construction of Nicol prism and show how it can be used as a polarizer and analyzer.
Answer
Sign in to view the complete answer paper.
At what wavelength, the given quarter wave plate for wavelength 600nm, will act as half wave plate.
Answer
Sign in to view the complete answer paper.
Obtain the relation between Einstein’s coefficients for probabilities of spontaneous and stimulated emission.
Answer
Sign in to view the complete answer paper.
Describe the construction and working of Ruby laser with a neat energy level diagram.
Answer
Sign in to view the complete answer paper.
What are different kinds of optical fibers? Discuss various kinds of dispersions produced when light propagates through optical fiber. Write down the three applications of optical fibers.
Answer
Sign in to view the complete answer paper.
Calculate the numerical aperture, acceptance angle and critical angle of a fiber having core refractive index 1.51 and cladding refractive index 1.45.
Answer
Sign in to view the complete answer paper.
Classify various lattice types in the cubic crystal system and specify the effective number of lattice point per unit cell in each type.
Answer
Sign in to view the complete answer paper.
Silver has FCC structure, and its atomic radius is 1.441 Å. Find the spacing of (2 2 0) planes.
Answer
Sign in to view the complete answer paper.
Describe in detail about the principle and process of Laue X-ray diffraction technique with a neat diagram.
Answer
Sign in to view the complete answer paper.
State and derive Bragg’s law. Calculate the longest wavelength that can be analyzed by rock salt crystal of spacing of 2.82 Å in the first order.
Answer
Sign in to view the complete answer paper.
What are Miller indices? Explain their role in the crystal structures. Draw the crystal planes having Miller indices (100), (111), (211).
Answer
Sign in to view the complete answer paper.
Determine the number of atoms per unit cell of lead which has an FCC structure. Atomic weight of Pb = 207.2, density of Pb = 11.36×10^3 kg/m^3 and a= 3.2 Å. Also NA = 6.023×10^26/kg mole.
Answer
Sign in to view the complete answer paper.
Specify three types of possible energy transitions between two atomic energy levels and derive conditions for Einstein’s coefficients.
Answer
Sign in to view the complete answer paper.
In a Laser, the total number of lasing particles are 2.8×10^19. If the Laser emits radiation of wavelength 7000 Å, then calculate the energy of one emitted photon and total energy available per pulse. Assume the efficiency of Laser to be 100%.
Answer
Sign in to view the complete answer paper.