## Applied Physics 2 - May 2013

### First Year Engineering (Semester 2)

TOTAL MARKS: 60

TOTAL TIME: 2 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **three** from the remaining questions.

(3) Use suitable data wherever required.

(4) Figures to the right indicate full marks.

### Attempt any five:-

**1 (a)** A glass material A with which an optical fibre is made has a refractive index of 1.55. This material is clad with another material whose refractive index of 1.51. The light in the fibre is launched from air. Calculate the numerical aperture of the fibre.(3 marks)
**1 (b)** Suppose that in a Newton^{ }s ring experiment, first light of red colour is used then blue, which sets of ring will have larger diameter? Justify your answer with proper expression.(3 marks)
**1 (c)** What is population inversion state? Explain its significance in operation of laser?(3 marks)
**1 (d)** In a plane transition grating, angle of diffraction for second order principle maximum for the wavelength 5 10^{-5} cm is 30°. Calculate the number of lines/cm of the grating surface.(3 marks)
**1 (e)** An electron is bound in a one dimensional potential well of width of 2Å, but of infinite height. Find its energy values in first excited surface.(3 marks)
**1 (f)** Explain the measurement of frequency of AC signal using CRO.(3 marks)
**1 (g)** Define superconductivity and explain critical magnetic field and critical temperature of a superconductor.(3 marks)
**2 (a)** With the help of proper diagram & necessary expression, explain how Newton^{ }s ring experiment can be used to determine the radius of curvature of a Plano convex lens. In a Newton^{ }s ring experiment the diameter of 5^{th} ring was 0.366cm and the diameter of 15^{th} ring is 0.590cm. Find the radius of radius of curvature of Plano-convex lens if the wavelength of light used is 5890Å.(8 marks)
**2 (b)** what is dispersion in optical fibres? Mention any 3 dispersion you have studied and explain any one in detail. Compute the maximum radius allowed for a fibre having core refractive index 1.47 and a cladding refractive index 1.46. The fibre is to support only one mode at a wavelength of 1300m.(7 marks)
**3 (a)** With a neat labelled diagram describe the construction and working of He-Ne laser. What are its merits & demerits.(8 marks)
**3 (b)** A plane wave of monochromatic light falls normally on a uniform thin film of oil, which covers a glass plate. The wavelength of the source is varied continuously. Complete destructive interference of reflected light is observed for 5000Å and 7000Å and for no other wavelength in between. Find the thickness of oil layer. Given refractive index of oil is 1.3 & glass is 1.5. (7 marks)
**4 (a)** Monochromatic light of wavelength 6560Å falls normally on grating surface 2cm wide. The first order spectrum is produced at an angle of 16°17^{'}from the normal. Calculate total number of lines on the grating.(5 marks)
**4 (b)** An electron has a speed of 400m/s with certain uncertainty of 0.01%. find the accuracy in position.(5 marks)
**4 (c)** Distinguish between type I & type II superconductors.(5 marks)
**5 (a)** Derive the condition for maximum spectra in diffraction grating.(5 marks)
**5 (b)** Show that the energy of electron in the box varies as square of natural numbers.(5 marks)
**5 (c)** What are the different techniques to synthesize nanomaterial? Explain one in detail.(5 marks)
**6 (a)** A bullet of mass 40 gms and an electron travel at a velocity of 1100m/s. What wavelengths can be associated with them? Why the wave nature of bullet is not revealed through diffraction effect.(5 marks)
**6 (b)** Derive Bethe's law for electron refraction.(5 marks)
**6 (c)** Explain the working of SEM with a neat diagram.(5 marks)