10 Question-Answer on lens aberrations
1. Chromatic aberration in a lens is caused by
(a) Reflection
(b) Interference
(c) Diffraction
(d) Dispersion.
Ans: (d)
2. Two lenses in contact form an achromatic lens. Their focal lengths are in the ratio 2:3. Their dispersive powers must be in the ratio of
(a) 1 : 3
(b) 2 : 3
(c) 3 : 2
(d) 3 : 1
Ans : (b)
3. An achromatic combination is to be obtained using a convex and a concave lens. The two lenses chosen should have
(a) Their powers equal
(b) Their refractive indices equal
(c) Their dispersive powers equal
(d) The product of their powers and dispersive powers equal.
Ans: (d)
4. Two lenses of focal lengths +10 cm and -15 cm when put in contact behave like convex lens. They will have zero longitudinal chromatic aberration, if ratio of dispersive powers is:
(a) +3/2
(b) +2/3
(c) -3/2
(d) -2/3
Ans: (b)
5. What is longitudinal spherical aberration in case of a lens which focuses central rays at 20.3 cm and marginal rays at 20.1 cm
(a) 0.2 cm
(b) 0.4 cm
(c) Zero
(d) None of these
Ans: (a)
6. Due to spherical aberration, the image is
(a) Blurred
(b) Coloured
(c) Both (a) and (b)
(d) Neither (a) nor (b)
Ans: (a)
7. In an eye piece, field lens and eye lens have focal lengths 7.5 cm and 7.3 cm. To eliminate spherical aberration, distance between them should be
(a) 0.2 cm
(b) 0.4 cm
(c) 0.1 cm
(d) 0.5 cm
Ans : (a)
8. In Ramsden eys piece, which aberrations is removed
(a) Spherical
(b) Chromatic
(c) Both
(d) Neither
Ans: (d)
9. In Huyghen’s eye piece, the aberrations removed are
(a) Spherical
(b) Chromatic
(c) Both
(d) Neither
Ans: (c)
10. What causes chromatic aberration?
(a) Marginal ray
(b) Central ray
(c) Difference in radii of curvature of its surfaces
(d) Variation of focal length of lens with colour.
Ans: (d)