1. What is the relationship between the focal length, f, of the objective and the resolving power of the telescope, R.P?
a) f ∝ R.P
b) f ∝ 1/R.P
c) f2 ∝ R.P
d) no relation
Explanation: For a telescope, the radius of the first dark ring = 1.22fλ/D
Therefore, the smaller will be the focal length of the objective, the sharper will be the diffraction pattern and hence the resolving power of the telescope would increase.
2. Which of the following does not show any interference pattern?
a) Soap bubble
b) Excessively thin film
c) A thick film
d) Wedge Shaped film
Explanation: An excessively thin film shows no interference pattern because in that case, as the thickness of the film is negligible, the path difference, Δ, between the two reflected rays turns out to be λ/2 which is the condition of minima. Hence, the pattern is not observed.
The interference pattern is observed in the soap bubble, thick film, and wedge-shaped film.
3. The main principle used in Interference is _____________
a) Heisenberg’s Uncertainty Principle
b) Superposition Principle
c) Quantum Mechanics
d) Fermi Principle
Explanation: Superposition principle is the basic principle used in the interference of light. When the incoming light waves superimpose constructively, the intensity increases while when they add destructively, it decreases.
4.When Two waves of same amplitude add constructively, the intensity becomes _____________
a) Double
b) Half
c) Four Times
d) One-Fourth
Explanation: As we know, I ∝ A2. Thus, as the two waves add constructively, their amplitude becomes twice and hence the intensity becomes four times.
5. The shape of the fringes observed in interference is ____________
a) Straight
b) Circular
c) Hyperbolic
d) Elliptical
Explanation: The fringes observed in an interference pattern are hyperbolic in shape. When the distance between the slits and the screen is large, they appear almost straight
6. If instead of monochromatic light white light is used for interference of light, what would be the change in the observation?
a) The pattern will not be visible
b) The shape of the pattern will change from hyperbolic to circular
c) Colored fringes will be observed with a white bright fringe at the center
d) The bright and dark fringes will change position
Explanation: When white light is used instead of monochromatic light, all the seven constituent colors produce their interference pattern. At the center of the screen, all the wavelengths meet in phase and, therefore, a white bright fringe is formed. Then the next fringe will be formed due to violet color as the wavelength is shortest for violet color. This will be followed by indigo, blue till red color.
7. Zero order fringe can be identified using ____________
a) White light
b) Yellow light
c) Achromatic light
d) Monochromatic light
Explanation: When the white light is used, the central fringe is white in color while the rest are colored. Thus, the central fringe can be identified using white light.
8. Interference is observed only when the phase difference between the two waves is zero.
a) True
b) False
Explanation: For interference pattern, the phase difference between the two rays must be constant. It is not necessary that the phase difference between the two rays has to be zero
9. The shape of the pattern depends on the ____________
a) Distance between the slits
b) Distance between the slits and the screen
c) Wavelength of light
d) Shape of the slit
Explanation: The shape of the interference pattern observed depends on the shape of the slits. If the shape of the slits changes, the shape of the fringes changes.
10. A thin sheet of refractive index 1.5 and thickness 1 cm is placed in the path of light. What is the path difference observed?
a) 0.003 m
b) 0.004 m
c) 0.005 m
d) 0.006 m
Explanation: AS we know, the path difference introduced by the sheet = (μ – 1) t, where t is the thickness of the sheet.
Here, μ = 1.5 and t = 0.01 m
Therefore, Δx = 0.5 X 0.01 m
= 0.005 m.