WAVE OPTICS
Very Short Question Answers
Q1. What is Fresnel distance?
Ans.The distance travelled by a beam of light before it starts to spread out due to diffraction is called Fresnel distance.
Fresnel distance
Where a = size of aperture, l= wavelength.
Q2. Give the justification for validity of ray optics.
Ans.Ray optics is valid only when the wave length of light (l) tends to zero.
(Or) when Fresnel distance
Q3. What is polarization of light?
Ans. The phenomenon of restricting the electric vectors flight into a single direction is called polarization.
Q4. What is Malus law?
Ans. The intensity (
Q5. Explain Brewsters law?
Ans. When light is incident at polarizing angle
Q6. When does a monochromatic beam of light incident on a reflective surface get completely transmitted?
Ans. When a monochromatic light beam passing through a polarizer is incident on the surface of a prism at Brewstar angle, then total transmission of light takes place through the prism for a particular alignment of the polarizer.
Short Question Answers
Q1. Explain Doppler Effect in light. Distinguish between red shift and blue shift.
Ans. Doppler Effect in Light: According to Doppler Effect, whenever there is a relative motion between a source of light andobserver, the apparent frequency of light received by the observer is different from the true frequency of light emittedactually from the source of light.
The apparent frequency of light increases when the distance between source of light and observer is decreasing and the apparent frequency of light decreases if the distance between source of light and observer is increasing.
Blue shift: When source and observer approach each other, △ υ is +ve, i.e., apparent frequency increases or apparent wavelength decreases. This is called "Blue shift".
Red shift: When source and observer recede away from each other, △ υ is +ve, i.e., apparent frequency increases or apparent
decreases or apparent wavelength increases. This is called "Red shift‟.
Q2. Derive the expression for the intensity at a point where interference of light occurs. Arrive at the conditions for
maximum and zero intensity.
Ans.
Condition for minimum intensity
Q3. How do you determine the resolving power of your eye?
Ans. In figure all the black stripes should be of equal width, while the width of the intermediate white stripes should
increase as you go from the left to the right. For example let all black stripes have a width of
Q4. Discuss the intensity of transmitted light when a Polaroid sheet is rotated between two crossed Polaroid.
Ans. Let I
through second polariser
Hence the intensity of light emerging from