TS Polycet (Polytechnic) 2021 Previous Question Paper with Answers And Model Papers With Complete Analysis

71) Object distance (u), image distance (v), focal length (f) are all measured form

A) focus (F)
B) optic centre (P)
C) Centre of curvature C.
D) Principal axis

View Answer

B) optic centre (P)

Explanation:optic centre (P)
(In optics, object distance (u), image distance (v), and focal length (f) are all measured from the optic centre (P) of the lens/mirror.)

72) In our eye cones identify.

A) Intensity of light
B) colour
C) Tate
D) Smell

View Answer

B) colour

Explanation:colour
(Cones in the human eye are responsible for color vision, while rods detect light intensity.)

73) With the help of …….eye-lens changes its focal length

A) Aqueous humor
B) Cornea
C) Ciliary muscle
D) Pupil

View Answer

C) Ciliary muscle

Explanation:Ciliary muscle
(The ciliary muscles help adjust the curvature of the eye-lens, changing its focal length for accommodation.)

74) A bird is flying down vertically towards the surface of water with constant speed. A fish in the water vertically below the bird sees the bird

A) Further away than actual distance
B) Closer than actual distance
C) At actual distance
D) In inclined positon

View Answer

A) Further away than actual distance

Explanation:Further away than actual distance
(Due to refraction at the water-air interface, the bird appears higher (farther away) than its actual position to the fish.)

75) Focal length of Plano-convex lens of refractive index n and radius of curvature R is

A) f=R
B) $f=\frac R2$
C) $f=\frac{n-1}R$
D) $f=\frac R{n-1}$

View Answer

D) $f=\frac R{n-1}$

Explanation:( f = $\frac{R}{n-1}$ )
(The focal length of a plano-convex lens with refractive index ( n ) and radius of curvature ( R ) is given by ( f = $\frac{R}{n-1}$ ).)

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