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Q. In an experiment to find out the diameter of wire using screw gauge, the following observation were noted :
image
(a) Screw moves $0.5 \,mm$ on main scale in one complete rotation
(b) Total divisions on circular scale $=50$
(c) Main scale reading is $2.5 \,mm$
(d) $45^{\text {th }}$ division of circular scale is in the pitch line
(e) Instrument has $0.03 \, mm$ negative error
Then the diameter of wire is :

JEE MainJEE Main 2022Physical World, Units and Measurements

Solution:

$ \text{MSR}=2.5 mm $
$ \text{CSR}=45 \times \frac{0.5}{50} mm $
$ =0.45 \,mm$
Diameter reading $=$ MSR $+$ CSR $-$ zero error
$ =2.5+0.45-(-0.03)$
$ =2.98 \,mm$