JEE Main · 2022 · 26 Jul 2022 · Shift 1 · Units & Measurement

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A screw gauge of pitch 0.5 mm is used to measure the diameter of uniform wire of length 6.8 cm , the main scale reading is 1.5 mm and circular scale reading is 7 . The calculated curved surface area of wire to appropriate significant figures is :
[Screw gauge has 50 divisions on the circular scale]

(A) $6.8 cm^{2}$
(B) $3.4 cm^{2}$ ✓ Correct
(C) $3.9 cm^{2}$
(D) $2.4 cm^{2}$

Answer: (B)

Solution

Least count:

L.C. = \frac{Pitch}{Divisions} = \frac{0.5}{50} = 0.01

mm

Diameter:

d = 1.5 + 7 \times 0.01 = 1.57

mm = 0.157 cm

Curved surface area:

A = π d ℓ = 3.14 \times 0.157 \times 6.8 = 3.352 \approx 3.4

cm²

The answer is (B) 3.4 cm².

JEE Main · 2022 · 26 Jul 2022 · Shift 1 · Single correct option

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