Q. An object is placed 50 cm from a converging lens of focal length 25 cm. Where will the image be formed?
A.
16.67 cm
B.
33.33 cm
C.
25 cm
D.
20 cm
Show solution
Solution
Using the lens formula 1/f = 1/v - 1/u, we find v = 33.33 cm.
Correct Answer:
B
— 33.33 cm
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Q. An object is placed at a distance of 40 cm from a convex lens of focal length 20 cm. Where will the image be formed?
A.
10 cm
B.
20 cm
C.
30 cm
D.
40 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, we find v = 10 cm.
Correct Answer:
A
— 10 cm
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Q. An object is placed at the focus of a concave lens. What type of image is formed?
A.
Real and inverted
B.
Virtual and erect
C.
Real and erect
D.
Virtual and inverted
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Solution
A concave lens always forms a virtual and erect image regardless of the object position.
Correct Answer:
B
— Virtual and erect
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Q. If a concave lens has a focal length of -10 cm, what is the nature of the image formed when the object is placed at 5 cm?
A.
Real and inverted
B.
Virtual and upright
C.
Real and upright
D.
Virtual and inverted
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Solution
Concave lenses always produce virtual and upright images.
Correct Answer:
B
— Virtual and upright
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Q. If a concave lens has a focal length of -10 cm, what is the nature of the image formed when an object is placed at 5 cm from the lens?
A.
Real and inverted
B.
Virtual and upright
C.
Real and upright
D.
Virtual and inverted
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Solution
Concave lenses always produce virtual and upright images.
Correct Answer:
B
— Virtual and upright
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Q. If a concave lens has a focal length of -20 cm, what is the nature of the image formed when an object is placed at 30 cm from the lens?
A.
Real and inverted
B.
Virtual and upright
C.
Real and upright
D.
Virtual and inverted
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Solution
For a concave lens, the image formed is virtual and upright when the object is placed beyond the focal length.
Correct Answer:
B
— Virtual and upright
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Q. If a concave lens has a focal length of -20 cm, what is the nature of the image formed when an object is placed at 30 cm?
A.
Real and inverted
B.
Virtual and upright
C.
Real and upright
D.
Virtual and inverted
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Solution
The image formed by a concave lens is virtual and upright when the object is placed beyond the focal length.
Correct Answer:
B
— Virtual and upright
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Q. If a lens forms a real image at a distance of 40 cm from the lens, and the object is placed at 60 cm, what is the focal length of the lens?
A.
15 cm
B.
20 cm
C.
25 cm
D.
30 cm
Show solution
Solution
Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/40 - 1/(-60) = 1/40 + 1/60 = 1/24. Therefore, f = 24 cm.
Correct Answer:
C
— 25 cm
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Q. If a lens has a power of -2 D, what is its focal length?
A.
-50 cm
B.
-25 cm
C.
25 cm
D.
50 cm
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Solution
Power (P) = 1/f, so f = 1/P = 1/(-2) = -0.5 m = -50 cm.
Correct Answer:
B
— -25 cm
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Q. If a lens has a power of -2 D, what type of lens is it?
A.
Convex lens
B.
Concave lens
C.
Bifocal lens
D.
Plano-convex lens
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Solution
A negative power indicates a concave lens.
Correct Answer:
B
— Concave lens
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Q. If the distance between the object and the image formed by a lens is 70 cm, and the object distance is 30 cm, what is the image distance?
A.
40 cm
B.
50 cm
C.
60 cm
D.
70 cm
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Solution
Image distance (v) = Object distance (u) + Distance between object and image = 30 cm + 70 cm = 40 cm.
Correct Answer:
A
— 40 cm
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Q. If the focal length of a lens is doubled, how does the power of the lens change?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Quadruples
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Solution
Power is inversely proportional to focal length. If f is doubled, P = 1/f will halve.
Correct Answer:
B
— Halves
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Q. If the image distance is equal to the object distance for a lens, what is the magnification?
A.
0
B.
1
C.
2
D.
Infinity
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Solution
Magnification (m) = v/u = 1 when image distance equals object distance.
Correct Answer:
B
— 1
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Q. If the image distance of a convex lens is 40 cm and the object distance is 30 cm, what is the focal length of the lens?
A.
10 cm
B.
20 cm
C.
30 cm
D.
15 cm
Show solution
Solution
Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/40 - 1/(-30) = 1/40 + 1/30. Solving gives f = 20 cm.
Correct Answer:
B
— 20 cm
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Q. If the object distance is equal to the focal length of a convex lens, what is the nature of the image formed?
A.
Real and inverted
B.
Virtual and upright
C.
At infinity
D.
No image formed
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Solution
When the object distance equals the focal length, the image is formed at infinity.
Correct Answer:
C
— At infinity
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Q. If the object distance is equal to the focal length of a convex lens, what type of image is formed?
A.
Real and inverted
B.
Virtual and upright
C.
At infinity
D.
No image formed
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Solution
When the object is at the focal length, the image is formed at infinity.
Correct Answer:
C
— At infinity
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Q. If the radius of curvature of a lens is 20 cm, what is the focal length of the lens assuming it is made of glass with a refractive index of 1.5?
A.
10 cm
B.
15 cm
C.
20 cm
D.
30 cm
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Solution
Using the lens maker's formula, f = R/(n-1) = 20/(1.5-1) = 40 cm.
Correct Answer:
A
— 10 cm
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Q. If the radius of curvature of a lens is 30 cm and the refractive index is 1.5, what is the focal length of the lens?
A.
10 cm
B.
15 cm
C.
20 cm
D.
25 cm
Show solution
Solution
Using the lens maker's formula, f = R/(n-1) = 30/(1.5-1) = 30/0.5 = 60 cm.
Correct Answer:
B
— 15 cm
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Q. If the radius of curvature of a lens is 30 cm, what is the focal length of the lens assuming it is made of glass with a refractive index of 1.5?
A.
10 cm
B.
15 cm
C.
20 cm
D.
25 cm
Show solution
Solution
Using the lens maker's formula, f = R/(n-1) = 30/(1.5-1) = 30/0.5 = 60 cm.
Correct Answer:
B
— 15 cm
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Q. In a compound microscope, which lens is the eyepiece?
A.
Convex lens
B.
Concave lens
C.
Bifocal lens
D.
Plano-convex lens
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Solution
The eyepiece of a compound microscope is a convex lens.
Correct Answer:
A
— Convex lens
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Q. In a compound microscope, which lens is the objective lens?
A.
The lens closest to the eye
B.
The lens closest to the object
C.
The lens with the longer focal length
D.
The lens with the shorter focal length
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Solution
The objective lens is the one closest to the object being viewed.
Correct Answer:
B
— The lens closest to the object
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Q. In a double convex lens, if the radii of curvature are 10 cm and 15 cm, what is the focal length using the lens maker's formula?
A.
6 cm
B.
10 cm
C.
12 cm
D.
8 cm
Show solution
Solution
Using the lens maker's formula, f = (R1 * R2) / (n - 1) * (1/R1 - 1/R2), we find f = 12 cm.
Correct Answer:
C
— 12 cm
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Q. What happens to the focal length of a lens when it is immersed in water?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes infinite
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Solution
The focal length of a lens decreases when immersed in a medium with a higher refractive index than air.
Correct Answer:
B
— Decreases
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Q. What happens to the image distance when the object is moved closer to a convex lens beyond its focal point?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes negative
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Solution
As the object moves closer, the image distance increases.
Correct Answer:
A
— Increases
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Q. What happens to the image formed by a convex lens when the object is moved closer to the lens than its focal length?
A.
Image disappears
B.
Image becomes real
C.
Image becomes virtual
D.
Image becomes inverted
Show solution
Solution
When the object is within the focal length of a convex lens, the image formed is virtual and upright.
Correct Answer:
C
— Image becomes virtual
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Q. What is the effect of increasing the curvature of a lens on its focal length?
A.
Focal length increases
B.
Focal length decreases
C.
Focal length remains the same
D.
Focal length becomes zero
Show solution
Solution
Increasing the curvature of a lens decreases its focal length.
Correct Answer:
B
— Focal length decreases
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Q. What is the effect of increasing the object distance on the size of the image formed by a convex lens?
A.
Image size increases
B.
Image size decreases
C.
Image size remains constant
D.
Image size becomes zero
Show solution
Solution
As the object distance increases, the size of the image formed by a convex lens increases until it reaches a maximum.
Correct Answer:
A
— Image size increases
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Q. What is the focal length of a convex lens if it forms a real image at a distance of 30 cm when the object is placed at 15 cm from the lens?
A.
10 cm
B.
15 cm
C.
20 cm
D.
25 cm
Show solution
Solution
Using the lens formula 1/f = 1/v - 1/u, where v = 30 cm and u = -15 cm, we find f = 20 cm.
Correct Answer:
C
— 20 cm
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Q. What is the focal length of a lens if it forms a virtual image at a distance of 15 cm when the object is placed at 10 cm?
A.
-30 cm
B.
30 cm
C.
15 cm
D.
10 cm
Show solution
Solution
Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/(-15) - 1/(-10) = -1/15 + 1/10 = -1/30, thus f = -30 cm.
Correct Answer:
A
— -30 cm
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Q. What is the focal length of a lens if it forms a virtual image at a distance of 12 cm when the object is placed at 8 cm?
A.
-24 cm
B.
-12 cm
C.
12 cm
D.
24 cm
Show solution
Solution
Using the lens formula, we find the focal length to be -12 cm.
Correct Answer:
B
— -12 cm
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Showing 31 to 60 of 78 (3 Pages)
Lenses MCQ & Objective Questions
Lenses are a crucial topic in physics that students encounter in their academic journey. Understanding lenses not only helps in grasping fundamental concepts but also plays a significant role in exam preparation. Practicing MCQs and objective questions on lenses can enhance your problem-solving skills and boost your confidence, leading to better scores in exams. Engaging with these practice questions will ensure you are well-prepared for important questions that frequently appear in assessments.
What You Will Practise Here
Types of lenses: Convex and concave
Lens formula and its applications
Ray diagrams for different lens types
Magnification and its significance
Real and virtual images
Numerical problems involving lenses
Key definitions and terminology related to lenses
Exam Relevance
The topic of lenses is frequently tested in various examinations such as CBSE, State Boards, NEET, and JEE. Students can expect questions that require them to apply the lens formula, draw ray diagrams, and solve numerical problems. Common question patterns include direct applications of the lens formula, conceptual questions about image formation, and problems that involve calculating magnification. Being well-versed in these areas will significantly enhance your performance in both school and competitive exams.
Common Mistakes Students Make
Confusing the properties of convex and concave lenses
Incorrectly applying the lens formula in numerical problems
Misinterpreting ray diagrams leading to wrong conclusions about image characteristics
Overlooking the sign conventions while calculating magnification
Neglecting to differentiate between real and virtual images
FAQs
Question: What is the lens formula?Answer: The lens formula is given by 1/f = 1/v - 1/u, where f is the focal length, v is the image distance, and u is the object distance.
Question: How do I determine if an image is real or virtual?Answer: An image is real if it can be projected on a screen and is formed on the opposite side of the lens from the object; it is virtual if it cannot be projected and is formed on the same side as the object.
Now is the time to sharpen your skills! Dive into our practice MCQs on lenses and test your understanding. Regular practice will not only clarify concepts but also prepare you for the important lenses questions you will face in your exams. Start solving today!
