Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main
Exam
JEE Main
Subject
Physics
Chapter
Experimental Physics

JEE Main · Physics · Experimental Physics

The pitch of a screw gauge is 1.0 mm and there are 100 divisions on...

The pitch of a screw gauge is 1.0 mm1.0 \text{ mm} and there are 100100 divisions on its circular scale. When the jaws of the screw gauge are completely closed, the zero mark of the circular scale is 77 divisions above the reference line. When a wire is placed between the jaws to measure its diameter, the main scale reading is 3.0 mm3.0 \text{ mm} and the 65th65^{\text{th}} division of the circular scale coincides with the reference line. The true diameter of the wire is:

Options

  1. A3.58 mm3.58 \text{ mm}
  2. B3.72 mm3.72 \text{ mm}
  3. C3.65 mm3.65 \text{ mm}
  4. D4.58 mm4.58 \text{ mm}

Correct answer

B. 3.72 mm3.72 \text{ mm}

Step-by-step solution

The least count (LC) of the screw gauge is:
LC=PitchTotal circular divisions=1.0100=0.01 mm\text{LC} = \dfrac{\text{Pitch}}{\text{Total circular divisions}} = \dfrac{1.0}{100} = 0.01 \text{ mm}

When the jaws are closed, the zero mark of the circular scale is above the reference line. This indicates a negative zero error.
Zero Error=−7×LC=−7×0.01=−0.07 mm\text{Zero Error} = -7 \times \text{LC} = -7 \times 0.01 = -0.07 \text{ mm}

The measured reading of the wire's diameter is:
Measured Value=MSR+(CSR×LC)\text{Measured Value} = \text{MSR} + (\text{CSR} \times \text{LC})
Measured Value=3.0+(65×0.01)=3.65 mm\text{Measured Value} = 3.0 + (65 \times 0.01) = 3.65 \text{ mm}

The true diameter is obtained by subtracting the zero error from the measured value:
True Value=Measured Value−Zero Error\text{True Value} = \text{Measured Value} - \text{Zero Error}
True Value=3.65−(−0.07)=3.65+0.07=3.72 mm\text{True Value} = 3.65 - (-0.07) = 3.65 + 0.07 = 3.72 \text{ mm}

Answer: 3.72 mm3.72 \text{ mm}
Practice Experimental Physics on Quantrex Academy →

More from Experimental Physics

Two thin wires, Wire-1 of diameter 0.650 mm and Wire-2 of unknown diameter d are given.… JEE Advanced 2026In a Vernier calipers, when both jaws touch each other, zero of the Vernier scale is… JEE Main 2026In a screw gauge when the circular scale is given five complete rotations it moves… JEE Main 2026In a screw gauge the zero of main scale reference line coincides with the fifth division… JEE Main 2026In an experiment, a set of reading are obtained as follows - 1.24 ~mm, 1.25 ~mm, 1.23 ~mm… JEE Main 2026When both jaws of vernier callipers touch each other, zero mark of the vernier scale is… JEE Main 2026In a vernier callipers, 50 vernier scale divisions are equal to 48 main scale divisions.… JEE Main 2026In a screw gauge, the zero of the circular scale lies 3 divisions above the horizontal… JEE Main 2026 Full Experimental Physics list All JEE Main PYQs