Test: Spherical Lens & its Power - UPSC MCQ

# Test: Spherical Lens & its Power - UPSC MCQ

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## 10 Questions MCQ Test Science & Technology for UPSC CSE - Test: Spherical Lens & its Power

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Test: Spherical Lens & its Power - Question 1

### The combination of a convex lens of power +2D and a concave lens of power -2D, acts as a

Detailed Solution for Test: Spherical Lens & its Power - Question 1

Net power =0
F=infinity
The emergent ray in the rectangular glass slab is parallel to the incident ray so the focal length of the glass slab is infinite.

Test: Spherical Lens & its Power - Question 2

### A person having myopic eyes uses a concave lens of focal length 50 cm. What is the power of the lens ?

Detailed Solution for Test: Spherical Lens & its Power - Question 2

So  focal length = - 50 cm = - 0.50 meter
power = - 1/0.50 = -2 Dioptre or - 2 D

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Test: Spherical Lens & its Power - Question 3

### The power of a lens of focal length 50 cm is

Detailed Solution for Test: Spherical Lens & its Power - Question 3

Power of a lens is always reciprocal to the focal length. So,  a convex lens with 50 cm focal length has a power of :- 1/0.5
⇒  2D

Test: Spherical Lens & its Power - Question 4

Power of a lens is

Detailed Solution for Test: Spherical Lens & its Power - Question 4

Power of a Lens
The power of a lens is its ability to bend light – the greater the power the greater the refraction of light.

The power of a lens is also related to the focal length by the following formula:

Power of a lens is measured in Dioptres (D).

Focal length is measured in metres (m).

Test: Spherical Lens & its Power - Question 5

SI unit of power of lens is

Test: Spherical Lens & its Power - Question 6

The objective lens of microscope use

Detailed Solution for Test: Spherical Lens & its Power - Question 6

The correct option is C.
The simplest compound microscope is constructed from two convex lenses. The objective lens is a convex lens of short focal length (i.e., high power) with typical magnification from 5× to 100×. The eyepiece, also referred to as the ocular, is a convex lens of longer focal length.

Test: Spherical Lens & its Power - Question 7

A spherical mirror and a thin spherical lens have each a focal length of -12 cm. The mirror and the lens are likely to be:

Detailed Solution for Test: Spherical Lens & its Power - Question 7

The focal length of concave mirror and lens is always negative.

Test: Spherical Lens & its Power - Question 8

Which one of the following is the use of convex lens

Test: Spherical Lens & its Power - Question 9

Which of the following term is not associated with a lens ?

Detailed Solution for Test: Spherical Lens & its Power - Question 9

Aperture of a lens is the length of the surface of lens exposed for incident light. Focal length is the distance between focus of the lens and lens optical center. There is no term like efficiency of a lens.

Test: Spherical Lens & its Power - Question 10

Two thin lenses of power +3.5 D and -2.5 D are placed in contact. Find the focal length of the lens combination.​

Detailed Solution for Test: Spherical Lens & its Power - Question 10

Power one of lens = P1 = +3.5D (Given)
Power two of lens = P2 = -2.5D (Given)
Power combination = P1 + P2

Thus,
Power of combination = +3.5 D +(-2.5 D )
= 3.5 D -2.5 D
= 1 D

Power = 1/focal length(m)
1 = 1/f
f = 1/1
f = 1 metre
Thus, the  f of combination = 1×100 = 100 cm

Therefore, if two thin lenses of power +3.5D and -2.5D are placed in contact then the power and focal length of the lens combination will be 100cm.

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