Magnification, Power of a Lens, Combination of thin lenses in contact. Refraction of light... NEET Questions

Physics - Optics

Magnification, Power of a Lens, Combination of thin lenses in contact. Refraction of light... MCQ Questions


13.
Two thin lenses of powers +3 D and -1 D are in contact. The total power is:
A.
+2 D
B.
-2 D
C.
+4 D
D.
+3 D
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ANSWER :
A. +2 D
14.
Three thin lenses of focal lengths 10 cm, 20 cm, and -25 cm are placed in contact. The power of the combination is:
A.
+5 D
B.
+11 D
C.
-1 D
D.
+19 D
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ANSWER :
B. +11 D
15.
Two thin lenses of focal lengths f and -f placed in contact behave as:
A.
A converging lens of focal length 2f
B.
A diverging lens of focal length 2f
C.
A plane glass plate (P = 0, f = ∞)
D.
A converging lens of focal length f/2
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ANSWER :
C. A plane glass plate (P = 0, f = ∞)
16.
When two thin lenses of focal lengths f₁ = +20 cm and f₂ = -10 cm are placed in contact, the system behaves as:
A.
A diverging lens of focal length 10 cm
B.
A converging lens of focal length 30 cm
C.
A converging lens of focal length 6.67 cm
D.
A diverging lens of focal length 20 cm
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ANSWER :
D. A diverging lens of focal length 20 cm
17.
Two equiconvex lenses each of focal length 20 cm are placed in contact. The equivalent focal length is:
A.
20 cm
B.
10 cm
C.
40 cm
D.
5 cm
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ANSWER :
B. 10 cm
18.
Total magnification of a combination of lenses equals:
A.
Sum of magnifications: m = m₁ + m₂ + m₃ + ...
B.
Product of individual magnifications: m = m₁ × m₂ × m₃ × ...
C.
Maximum of individual magnifications
D.
Square root of sum of squares
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ANSWER :
B. Product of individual magnifications: m = m₁ × m₂ × m₃ × ...