Light (Physics) (Part-2)

Total Questions: 10

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

Correct Answer: (c) Iris
Solution:

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

Eye Anatomy - Exeter Eye

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-I)]

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.

Parts of a Microscope with Functions and Labeled Diagram

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.
P=1/f
(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-I) 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.
P=1/f
(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-I) 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:
f = 15/100 = 0.15 m
Now calculate the power:
6.67 diopters (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-I) 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%.