56. The limit of resolution of an optical instrument arises on account of :
(a) Reflection
(b) Interference
(c) Diffraction
(d) Polarisation
Answer:
(c) Diffraction
Explanation:
Diffraction causes light passing through an aperture to spread out, turning point sources into diffraction patterns (Airy disks). The overlapping of these disks fundamentally limits the resolution of any optical instrument.
57. Which of the following phenomenon is used in optical fibres ?
(a) Dispersion
(b) Refraction
(c) Interference
(d) Total Internal Reflection
Answer:
(d) Total Internal Reflection
Explanation:
Optical fibers transmit light over long distances by keeping the light trapped inside the core via total internal reflection against the cladding boundary.
58. Refractive index of a material is greatest for:
(a) Blue light
(b) Red light
(c) Violet light
(d) Same for all colours
Answer:
(c) Violet light
Explanation:
According to Cauchy’s equation, refractive index increases as wavelength decreases. Violet light has the shortest wavelength in the visible spectrum, so it experiences the highest refractive index.
59. Which of the following graphs represent the variation of particle momentum associated with de Broglie wavelength ? https://canva.link/8kx8otsxwjhqdhx
Answer:
(c) Rectangular hyperbola
Explanation:
The de Broglie relation is , which means momentum . Since momentum is inversely proportional to wavelength, the graph of versus is a rectangular hyperbola.
60. The activity of a radioactive material decreases to 75% of the initial value after 30 days. The half-life of the material is approximately : [Take In $3 = 1.1$, In $4 = 1.4$]
(a) 45 days
(b) 69 days
(c) 93 days
(d) 127 days
Answer:
(b) 69 days
Explanation:
Using the decay law , we have . Taking the natural log gives per day. Half-life days.
