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Light (Part -2)

📆 December 6, 2024

Total Questions: 10

1. The amount of light entering into eye can be controlled and regulated by________. [S.S.C. Online Graduation Level (T-1) 4.06.2019 (Shift-III)]

Correct Answer: (a) iris
Solution:

The amount of light entering into the eye can be controlled and regulated by the iris.

2. Which of the following is NOT necessarily a part of a school laboratory compound microscope? [S.S.C. JE Mechanical Exam 22.03.2021 (Shift-1)]

Correct Answer: (d) Camera
Solution:Eye-piece, objective lens, and mirror are essential parts of the compound microscope of the school laboratory, while the camera is not a necessary part of it.

3. Diopter is the SI of which of the following? [S.S.C. Online Stenographer 13.09.2017 (Shift-II)]

Correct Answer: (c) power of the lens
Solution:The SI unit of lens power is a diopter. The power of a convex lens is positive and that of a concave lens is negative.
(f in meters)
where
P = power of lens.
f = focal length of the lens.

4. What is the SI unit of lens power? [S.S.C. Online MTS (T-1) 5.08.2019 (Shift-II)]

Correct Answer: (d) diopters
Solution:The SI unit of lens power is a diopter. The power of a convex lens is positive and that of a concave lens is negative.
(f in meters)
where
P = power of lens.
f = focal length of the lens.

5. The power of a lens is 2.0 D. Here 'D' stands for : [S.S.C. Online Graduation Level (T-1) 7.03.2020 (Shift-I)]

Correct Answer: (a) Dioptre
Solution:The unit of power of a lens is expressed by diopter (D).

6. Find the power of a convex lens, if the image is formed at a distance of 20 cm from the lens when the object is placed at a distance of 60 cm from the optical center on the other side of the lens? [S.S.C. Online CHSL (T-I) 31.01.2017 (Shift-III)]

Correct Answer: (b) 6.67 diopters
Solution:

To find the power of a convex lens, we use the lens formula and the power formula. Let's solve this step by step.
Given that

  • Image distance (v) = +20 cm (positive for a real image formed on the other side of the lens)
  • Object distance () = -60 cm (negative as per the sign convention for the object distance)
  • Focal length (f) needs to be calculated first, then power () will be derived.
    Step 1: Lens Formula

    The lens formula is: (1/f) = (1/v) - (1/u)
    (1/f) = (1/20) - (1/-60)
    Simplifying 
    (1/f) = (1/20) + (1/60) = (4/60) = (1/15)
    So, the focal length f is:
    f=+15 cm
    (The positive sign indicates a convex lens.)

    Step 2: Power of the Lens

    The power P of a lens is given by:
    P=1/f (in meters)
    Convert the focal length from centimeters to meters:
    6.67diopters (D)

7. Find the power of a convex lens if the image formed is at a distance of 20 cm from the lens when the object is placed on the other side of the lens at 25cm from the optical centre? [S.S.C. Online CHSL (T-1) 31.01.2017 (Shift-I)]

Correct Answer: (c) 9 diopters
Solution:To find the power of a convex lens, we need to determine its focal length and then use the power formula. Let's solve this step-by-step using the lens formula.
Given that :
  • Object distance, u = −25 cm.
  • Image distance, v = +20 cm. 
  • Lens formula: 1/f = (1/v) − (1/u)
    = (1/20) - (1/-25) = (1/20) + (1/25)
    = (5 + 4)/100 = 9/100
    ∴ f = 100/9 cm
    Then P = 1/f (f in metres)
    = 1/100/(9 × 100) ⇒ 9 diopters

8. Find the power of a convex lens if the image formed is at a distance of 16 cm from the lens when the object is placed on the other side of the lens at 20 cm from the optical centre? [S.S.C. Online CHSL (T-I) 2.02.2017 (Shift-I)]

Correct Answer: (d) 11.25 diopters
Solution:To find the power of a convex lens, we need to determine its focal length and then use the power formula. Let's solve this step-by-step using the lens formula.
Given that :
  • Object distance, u = −20 cm.
  • Image distance, v = +16 cm. 
  • Lens formula: 1/f = (1/v) − (1/u)
    = (1/16) - (1/-20) = (1/16) + (1/20)
    = (5 + 4)/80 = 9/80
    ∴ f = 80/9 cm
    Then P = 1/f (f in metres)
    = 1/80/(9 × 100) ⇒ (100 × 9)/80 ⇒ 11.25 diopters
    The power of the lens is positive.

9. Find the power of a convex lens if the image formed is at a distance of 10 cm from the lens when the object is placed on the other side of the lens at 40cm from the optical centre? [S.S.C. Online CHSL (T-I) 30.01.2017 (Shift-I)]

Correct Answer: (a) 12.5 diopters
Solution:To find the power of a convex lens, we need to determine its focal length and then use the power formula. Let's solve this step-by-step using the lens formula.
Given that :
  • Object distance, u = −40 cm.
  • Image distance, v = +10 cm. 
  • Lens formula: 1/f = (1/v) − (1/u)
    = (1/10) - (1/-40) = (1/10) + (1/40)
    = (4+1)/40 = 5/40 ⇒ 1/8 cm
    ∴ f = 40/5 cm ⇒ 8 cm
    Then P = 1/f (f in metres)
    = 1/8/100 ⇒ (100)/8 ⇒ 12.5 diopters
    The power of the lens is positive.

10. Which of the following reflects more sunlight than the other three? [C.P.O. S.I. 5.06.2016 (Shift-I)]

Correct Answer: (b) land covered with fresh snow
Solution:The land covered with fresh snow reflects more sunlight than the other three given in the alternatives.
sand desert = 20-30%
plain land = 25%
land covered by fresh snow = 85%
Paddy cropland = 20-25%.
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