Optics Answers

A ball is dropped from rest out of a high window in a tall building for 5 seconds. Assuming we ignore air resistance and assume upwards to be positive. A) What will be the final velocity of the ball B) What is the height of the building if it hits the ground after those 5 seconds.

Total internal reflection in prisms can be used to efficiently bend the light path in optical instruments such as cameras, binoculars, and microscopes.

What is the minimum refractive index of the material the prism is made of in the above diagram? (to 3 s.f)

[Note: the light enters and leaves the prism perpendicular to the faces]

The refractive indices of the core and cladding materials of an optical fibre are 1.64  and 1.53 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 5.0×10¹⁴ 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 600 K. Take k_b = 1.38×10^-23JK^-1 and h=6.6×10^-34Js.

Why pumping is necessary for laser action? Compare and contrast three level and four level pumping schemes for lasers.

An atomic system consisting of two energy levels with population of higher energy level less than that of the lower level, is in thermal equilibrium. Show that the absorption of radiation dominates stimulated emission if radiation of appropriate frequency is introduced into the system. Comment on the consequences of this fact for laser action.

 A beam of parallel light of wavelength 6000 Å is incident normally on a 1 rupee  coin of diameter 3 cm. If an observation screen is placed at a distance of 1 m from  the coin, how many Fresnel zones would be obstructed by it (the coin)? For what  separation between the coin and the screen, only 5 zones would be cut off?

6 principal maxima are observed in the diffraction pattern due to a diffraction grating. Calculate the number of lines per cm in the grating if the wavelength of the light is 5000 Å.

A grating has 10,000 lines per cm. What is the maximum number of principal  maxima that can be formed for light of wavelength 5×10^-5 cm?

Derive an expression for the intensity of the diffraction pattern obtained due to Fraunhofer diffraction from a single slit.