Q1. If the radius of curvature of a convex lens is 20 cm, what is its focal length? (2022)
Solution:
The focal length f of a lens is given by f = R/2. Therefore, f = 20 cm / 2 = 10 cm.
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Q2. What happens to the image distance when the object distance is increased in a convex lens? (2022)
Solution:
As the object distance increases in a convex lens, the image distance also increases, moving further away from the lens.
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Q3. A lens has a focal length of 15 cm. What is the power of the lens? (2023)
Solution:
Power (P) of a lens is given by P = 1/f (in meters). Here, f = 15 cm = 0.15 m, so P = 1/0.15 = +6.67 D.
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Q4. What is the focal length of a concave mirror if the object distance is 30 cm and the image distance is 15 cm? (2021)
Solution:
Using the mirror formula, 1/f = 1/v + 1/u. Here, v = -15 cm (real image) and u = -30 cm (object distance). Thus, 1/f = 1/(-15) + 1/(-30) = -1/10, so f = -10 cm.
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Q5. What type of image is formed by a convex lens when the object is placed beyond the 2F point? (2022)
Solution:
When the object is placed beyond 2F, the image formed by a convex lens is real, inverted, and smaller than the object.
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Q6. What type of image is formed by a plane mirror? (2021)
Solution:
A plane mirror always forms a virtual and erect image, which is the same size as the object.
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Q7. Which of the following statements is true for a concave lens? (2019)
Solution:
A concave lens diverges light rays, and it has a negative focal length.
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Q8. A ray of light passes through the center of curvature of a concave mirror. What will be the nature of the image formed? (2020)
Solution:
When a ray passes through the center of curvature, it reflects back on itself, forming a real and inverted image at the same distance as the object.
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Q9. What happens to the image when an object is moved closer to a convex lens than its focal length? (2019)
Solution:
When the object is placed within the focal length of a convex lens, the image formed is virtual and erect.
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Q10. A diverging lens has a focal length of -15 cm. What is the nature of the image formed when an object is placed at 10 cm from the lens? (2023)
Solution:
A diverging lens always forms a virtual and upright image when the object is placed in front of it.
