Fresnels Biprism Experiment Questions and Answers for Viva

Answer-1: The prism obtained by placing the two right angled prisms of very small refracting angle base to base, is called a biprism.

Answer-2: Two sources of light are said to be coherent if the waves emitted from them have the same frequency and are phase-linked; that is, they have a zero or constant phase difference.

Answer-3: By the division of wave front (by refraction of a wave front obtain from one light source through the biprism.

Answer-4: No, the reason is that the phase difference between the waves obtained from two independent light sources is not same; hence these waves are not coherent.

Answer-5: Sodium lamp. The reason is that the light emitted from it is nearly monochromatic.

Answer-6: Because, first the neon gas enclosed in it gets discharged.

Answer-7: So that the distance 2d between the two coherent sources formed by refraction, is small and the fringe width is large.

Answer-8: The fringes are formed in the region where the light cones coming from the two coherent sources superimpose.

Answer-9: No, the reason is that with the monochromatic source, all the bright fringes are of same colour. To locate the central fringe white light source is used in place of sodium lamp, then the central fringe will be white and the other fringes will be coloured.

Answer-10: Hyperbolic, but due to large eccentricity, the fringes appear to be nearly straight.

Answer-11: The shifting of the fringes across the optical bench when eye piece is moved towards or away from the biprism is called the lateral shift.

Answer-12: The lateral shift shows that the line joining the centre of slit and the edge of prism is not parallel to the bed of optical bench.

Answer-13: Yes, fringes are equally spaced.

Answer-14: The slit is made narrow to obtain good contrast of the interference fringes.

Answer-15: No, there is no loss of energy, but energy is simply redistributed. The energy from the places of minimum intensity is transferred to the places of maximum intensity.

Answer-16: It conforms us the wave nature of light.

Answer-17: The bans of alternate maximum and minimum intensities obtained in the region of superposition of two waves, are called the interference fringes.

Answer-18: It consists of a glass tube of U shape containing the pieces of sodium and neon gas at a pressure of nearly 10mm of mercury .There are two electrodes of tungsten coated with barium oxide . The tube is kept enclosed in an evacuated jacket so that there may not be any heat loss.

Answer-19: The reason is that initially when the vapour pressure is low, there is no discharge through the sodium .First the temperature is raised by discharge through the neon gas so that more sodium gets vaporized and then discharge takes place through sodium.

Answer-20: The phenomenon of interference is due to superposion of two waves coming from two different coherent light sources. While the phenomenon of diffraction of is due to superposition of secondary wavelets originated from each point of the exposed part of the incident wave front from the obstacle.

Answer-21: No, actually it is made from a single glass plate, with its two refracting angles very small (each nearly 30') and remaining angle very large (nearly 179⁰)

Answer-22: So that the distance 2d between the two coherent sources formed by refraction, is small and fringe width is large.