Question

Which of the following is most accurate?

• A. A screw gauge of least count 0.001 mm
• B. A screw gauge having pitch 1 mm and 50 divisions on circular scale
• C. A vernier callipers of least count 0.01 mm
• D. Vernier callipers having 20 divisions on the sliding scale (vernier scale) coinciding 19 divisions on the main millimetre scale.

Answer 1

The correct option is A A screw gauge of least count 0.001 mm

For A : Least count given $(L.C{)}_A=0.001mm$

For B : Least count $(L.C{)}_B=$ pitch/number of circular divs $=1/50=0.02mm$

For C : Least count given $(L.C{)}_C=0.01mm$

For D : $(L.C{)}_D=$ $1MSD-1VSD$

Here $20VSD=19MSD$ or $1VSD=19/20$ and in main millimeter scale $1MSD=1mm$

Thus, $(L.C{)}_D=(1-19/20)MSD=1/20\times 1mm=0.05mm$

As least count of A is smallest so it will measure the smallest length and so it is more accurate.