Q1. Which of the following statements is true for a plane mirror? (2023)
Solution:
A plane mirror always forms a virtual image that is the same size as the object and is erect.
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Q2. What is the focal length of a concave mirror if the object is placed at a distance of 30 cm and the image is formed at a distance of 15 cm from the mirror? (2021)
Solution:
Using the mirror formula, 1/f = 1/v + 1/u. Here, v = -15 cm (image distance is negative for concave mirror) and u = -30 cm. Therefore, 1/f = 1/(-15) + 1/(-30) = -1/10. Thus, f = 10 cm.
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Q3. A lens has a focal length of -15 cm. What type of lens is it? (2020)
Solution:
A negative focal length indicates that the lens is a concave lens.
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Q4. In a concave lens, the focal length is always: (2020)
Solution:
The focal length of a concave lens is always negative, as it diverges light rays.
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Q5. Which of the following statements is true about the image formed by a plane mirror? (2022)
Solution:
The image formed by a plane mirror is virtual, erect, and located behind the mirror at the same distance as the object.
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Q6. In a double convex lens, if the focal length is 15 cm, what is the power of the lens? (2022)
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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Q7. In a concave lens, the focal length is considered to be: (2023)
Solution:
The focal length of a concave lens is considered negative as it diverges light rays.
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Q8. What happens to the image distance when the object is moved closer to a concave mirror? (2021)
Solution:
As the object moves closer to a concave mirror, the image distance increases, and the image becomes larger and more distant.
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Q9. Which of the following statements is true about the image formed by a concave lens? (2023)
Solution:
A concave lens always forms a virtual image regardless of the position of the object.
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Q10. What is the critical angle for a medium with a refractive index of 1.5? (2019)
Solution:
The critical angle θc can be calculated using sin(θc) = 1/n. Thus, θc = sin^(-1)(1/1.5) = sin^(-1)(0.6667) ≈ 41.81 degrees, which is closest to 60 degrees.
