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

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) $\frac{n^2}v+\frac{n_1}u=\frac{n_2-n_1}R$

View Answer

A) $\frac{n^2}v-\frac{n_1}u=\frac{n_2-n_1}R$

Explanation: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 ).)

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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