Optics Answers

Why central rings in the Newton's ring always be dark.

Describe polarisation of light by reflection. How does degree of polarisation vary with angle of incidence of light?

Obtain an expression for elliptically polarised light resulting due to superposition of two orthogonal linearly polarised light waves

The refractive indices of the core and cladding materials of an optical fibre are 1.51 and 1.39 respectively. Calculate the numerical aperture and light gathering capacity of the fibre.

Two energy levels of an atomic system are separated by energy corresponding to frequency 3.0 × 1014 Hz. Assume that all atoms are in one or the other of these two energy levels, compute the fraction of atoms in the upper energy level at temperature 400 K. Take kB = 1.38×10−23JK−1 and h = 6.6×10−34Js.

Show that plane polarised light and circularly polarised light are special cases of elliptically polarised light.

A plane light wave of wavelength 580 nm falls on a long narrow slit of width 0.5 mm. (i) Calculate the angles of diffraction for the first two minima. (ii) How are these angles influenced if the width of slit is changed to 0.2 mm? (iii) If a convex lens of focal length 0.15 m is now placed after the slit, calculate the separation between the second minima on either side of the central maximum.

A plane light wave of wavelength 580 nm falls on a long narrow slit of width 0.5 mm. (i) Calculate the angles of diffraction for the first two minima. (ii) How are these angles influenced if the width of slit is changed to 0.2 mm? (iii) If a convex lens of focal length 0.15 m is now placed after the slit, calculate the separation between the second minima on either side of the central maximum.

A plano-convex lens of radius 1.0 m is placed on an optically flat glass plate and is illuminated by an extended monochromatic source. Assume that the point of contact is perfect. The diameters of the 10th and 5th dark rings in the reflected light are 4.50 × 10−3m and 3.36 × 10−3m. Next, the space between the lens and the glass plate is filled with a liquid. The diameter of the 5th ring changes to 3.0×10−3m. Calculate the refractive index of the liquid when the ring is (i) dark, and (ii) bright, if the wavelength of light is 589 nm.

An object 10 cm in front of a concave mirror forms an image
5 cm behind the mirror. What is the focal length of the mirror?