The distance between the first and the sixth bright fringes formed in Young’s double slit experiment (measured by a spectrometer) is found to be 12.5 mm. The separation between the slits is 0.12 mm and the distance of the screen from the slits is 60 cm. Calculate :
(i) the fringe width
(ii) the wavelength of the light used (in nm).
(i) What is the difference between the electric field vector E at any point in the path of a linearly polarized light and that of an un-polarized light ?
(ii) Briefly describe how a given beam of light can be analysed and determined if it is linearly polarized or un-polarized.
(i)
In linearly polarised light electric field vector vibrates along a fixed line in a plane perpendicular to the direction of propagation whereas in unpolarized light the electric field vector vibrates in any direction.
(ii)
The tourmaline crystal or Nicol prism used to produce plane polarised light is called polariser. If the polarizer is rotated in the path of the ordinary light, the intensity of the light transmitted from the polariser remains unchanged. It is because, in each orientation of the polarizer, the plane polarised light is obtained, which has vibrations in a direction parallel to the axis of the crystal in that orientation.
If the analyser is rotated in the path of the light transmitted from the polariser, to that the axes of the polarizer and the analyser are parallel to each other, then the intensity of light is found to remain unaffected (or maximum) as shown in figure
On the other hand, the intensity of light becomes minimum, when the axis of the polariser and the analyser are perpendicular to each other as shown in figure.
In the position shown in figure the polariser and the analyser are said to be in crossed positions.
A plano-convex lens made of glass (n = 1 5) has a focal length 10.0 cm.
(i) Calculate the radius of curvature of its curved surface.
(ii) If an identical plano-convex lens is placed in contact with the first (plane surfaces facing each other), what will be the power of the combination (in dioptres) ?
(i) State the three conditions for the formation of a pure spectrum.
(ii) Draw the ray diagram illustrating the measurement of the angle of a prism using a spectrometer.
The work function for sodium is 2.28 eV. [3]
(i) What is the minimum energy for a quantum of radiation to cause photoelectric emission from a sodium surface ?
(ii) Calculate the wavelength of this radiation.