Optics Answers

With the help of a diagram, explain the working of Michelson interferometer.  Explain how Michelson interferometer can be used for determining the refractive  index of a thin plate.

Interference fringes are produced by a beam of monochromatic light incident normally on a wedge shaped film of refractive index 1.5. The angle of the wedge is 15 seconds of an arc and the two successive dark fringes are 0.4 cm apart. Calculate the wavelength of light.

A wedge shaped film is obtained by placing a thin wire between two plane glass  plates at one end keeping them in contact with each other at the other end. When  the film is illuminated by light of wavelength 6000 Å, 40 fringes are observed.  Calculate the radius of the wire.

The wavelength of light used in Young’s double slit experiment is 6000 Å. The 

second and the fourth bright fringes from the centre of the fringe pattern are 

located respectively at 10.24 mm and 12.40 mm. If the observation screen is placed 

at a distance of 1 m from the slits, calculate the separation between the slits.

For a crystal, the refractive index n_o for the o-ray is 1.5442 for light of wavelength 

6×10^-5 m. The least thickness of the crystal used as a quarter wave plate is found to 

be 1.65×10^-5 m. Determine the refractive index ne for the e-ray in this crystal.

Two plane polarised light waves are propagating along the positive z-direction 

such that their electric field vectors are mutually perpendicular. These waves are 

superposed. Obtain the condition under which the resultant wave will be circularly 

polarised.

A beam of light is propagating in vacuum and its frequency is constant. Show that 

the average energy carried by it per unit area is proportional to the associated 

electric field vector.

State and explain Fermat’s principle. Using this principle, derive Snell’s law of 

refraction.

 A person jumps from a fourth story window 15.0 m above a firefighter’s safety net. 

The survivor stretches the net 1.0 m before coming to rest, Fig. 3. 

(a) What was the average deceleration experienced by the survivor when she was slowed 

to rest by the net? (5)

A modern mobile phone screen has pixels around 5.0 µm across.

We wish to make a telescope with a diffraction-limited angular resolution the same as the angular size of each pixel on your mobile phone screen when you are holding your phone 50 cm from your face. How large must the aperture of the telescope be? (to 2 s.f and in cm)

[Note: assume a wavelength of 500 nm.]