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

A) A

B) B

C) C

D) D

View Answer

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

76) A convex lens from image of an object at infinity. Object is at

A) focus (F)

B) C=2f

C) infinity

D) pole (P)

View Answer

A) focus (F)
Explanation:focus (F)
(For a convex lens, an object at infinity forms an image at the focal point (F).)

77) Formula used when a light ray enters a medium of refractive index n2 from a medium of refractive index at curved surface with radius n1 of curvature R is
A) $\frac{n^2}v-\frac{n_1}u=\frac{n_2-n_1}R$
B) $v-u=\frac{n_2-n_1}R$
C) $\frac v{n_2}-\frac u{n_1}=\frac{n_2-n_1}R$
D) $\frac{n^2}v+\frac{n_1}u=\frac{n_2-n_1}R$

:Correct:A
:MsgCorrect:A. ( $\frac{n_2}{v} - \frac{n_1}{u} = \frac{n_2 - n_1}{R}$ )
(This is the formula for refraction at a curved spherical surface separating two media with refractive indices ( n₁ ) and ( n₁ ).)
:MsgIncorrect:
:hint:

View Answer

78) 4Ω, 8Ω, R resistors are connected in series. Resultant resistance is 20Ω. Then R=

A) 6Ω

B) 4Ω

C) 18Ω

D) 8Ω

View Answer

B) 4Ω
Explanation:8Ω
(In series, resistances add up: ( 4Ω + 8Ω + R = 20Ω ) → ( R = 8Ω ).)

79) When how much current flows in the fuse, it melts

A) 200 A

B) 2 A

C) 20 A

D) 2000 A

View Answer

C) 20 A
Explanation:20 A
(A typical fuse melts when the current exceeds its rated value, often around 20 A for household applications.)

80) The alloy made of Cu, Mn, Ni is

A) Magnesium

B) Magnet

C) Manganin

D) Magma

View Answer

C) Manganin
Explanation:Manganin
(Manganin is an alloy made of copper (Cu), manganese (Mn), and nickel (Ni), known for its stable resistance.)

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