Question

Which of the following is the most precise device for measuring length?a. A vernier callipers with 20 divisions on the sliding scaleb. A screw gauge of pitch 1 mm 100 divisions on the circular scalec. An optical instrument that can measure length to within a wavelength of light

Answer 1

Given :

The most precise device is the one whose least count is least – minimum  

a) Least count of vernier calipers= 1 SD – 1VD

       =1SD-19/20 SD

=1/20 SD

=1/20 mm

=1/200 cm

=0.005cm

b) Least count = pitch/ number of divisions on circular scale

=1/100 mm

=1/1000 cm

=0.001cm

C] wavelelngth =10⁻⁵cm=0.00001cm

Clearly the optical instrument is most  precise  because its least count  is least.

Answer 2

Hii dear,

# Answer- Optical instrument

# Explaination-
First we'll calculate least count for all instruments.

(a) Least count vernier callipers
= 1MSD – 1 VSD
= 1 MSD – 19/20 MSD
= 1/20 MSD
= 1/20 mm
= 0.05 mm
= 0.005 cm

(b) Least count of screw gauge
= Pitch/Number of divisions
= 1/1000
= 0.001 cm.

(c) Least count of optional instrument
= Wavelength of light
= 10^-7 m
= 0.00001 cm

Precision is determined by the least count of an instrument.
Clearly optical instrument have lowest least count, so that will be most precise.

Hope that helps you.