physics : class12 Net diverging combination : Combination of Thin Lenses in Contact : Optics MCQ Questions and Answers
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Net diverging combination
MCQ questions and answers.
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MCQ Questions
1. A combination of two thin lenses in contact has powers +2 D and -5 D. What is the power of the combination?
A.
-7 D
B.
-3 D
C.
+3 D
D.
+7 D
Correct Answer:
-3 D
Explanation:
For thin lenses in contact, powers add: P = P1 + P2 = +2 D - 5 D = -3 D. The negative power shows that the combination is net diverging.
2. What is the nature of a lens combination whose net power is negative?
A.
Net converging
B.
Net diverging
C.
Plane-parallel
D.
Reflecting
Correct Answer:
Net diverging
Explanation:
A negative net power corresponds to a negative focal length, so the combination behaves as a net diverging lens.
3. Two thin lenses of powers +4 D and -6 D are placed in contact. What is the focal length of the combination?
A.
+0.5 m
B.
-0.5 m
C.
+2 m
D.
-2 m
Correct Answer:
-0.5 m
Explanation:
The net power is P = +4 D - 6 D = -2 D. Therefore, f = 1/P = 1/(-2) m = -0.5 m, indicating a net diverging combination.
4. A convex lens of power +3 D is combined with a concave lens of power -5 D in contact. Which type of combination is formed?
A.
Net converging combination
B.
Net diverging combination
C.
Zero-power combination
D.
Plane mirror combination
Correct Answer:
Net diverging combination
Explanation:
The net power is +3 D + (-5 D) = -2 D. Since the net power is negative, the combination is net diverging.
5. For a net diverging combination of thin lenses in contact, the equivalent focal length is:
A.
Positive
B.
Negative
C.
Always zero
D.
Always infinite
Correct Answer:
Negative
Explanation:
A net diverging combination has negative power. Since P = 1/f, its equivalent focal length is negative.
6. Two lenses in contact have powers -2 D and -3 D. What is the power of their combination?
A.
+1 D
B.
-1 D
C.
-5 D
D.
+5 D
Correct Answer:
-5 D
Explanation:
The powers of lenses in contact add algebraically: P = -2 D + (-3 D) = -5 D. Thus, the combination is net diverging.
7. A lens combination in contact has a net power of -4 D. What is its equivalent focal length?
A.
-0.25 m
B.
+0.25 m
C.
-4 m
D.
+4 m
Correct Answer:
-0.25 m
Explanation:
Using f = 1/P, the equivalent focal length is f = 1/(-4) m = -0.25 m. The negative value confirms the net diverging nature.
8. A convex lens of power +6 D is placed in contact with a concave lens of power -8 D. What is the net power?
A.
+14 D
B.
-14 D
C.
+2 D
D.
-2 D
Correct Answer:
-2 D
Explanation:
The net power is the algebraic sum: P = +6 D + (-8 D) = -2 D. Therefore, the combination is net diverging.
9. Which condition makes a combination of two thin lenses in contact net diverging?
A.
The positive power is greater than the negative power in magnitude
B.
The negative power is greater than the positive power in magnitude
C.
Both lens powers must be positive
D.
Both lens powers must be zero
Correct Answer:
The negative power is greater than the positive power in magnitude
Explanation:
The combination is net diverging when the algebraic sum of powers is negative. This occurs when the magnitude of the negative power exceeds the positive power.
10. A net diverging combination of lenses has an equivalent focal length of -0.2 m. What is its net power?
A.
-5 D
B.
+5 D
C.
-0.2 D
D.
+0.2 D
Correct Answer:
-5 D
Explanation:
Using P = 1/f, P = 1/(-0.2) D = -5 D. The negative power is consistent with a net diverging combination.
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