A student measured the diameter of a small steel ball using a screw gauge of least count 0.001 cm. The main scale reading is 5 mm and zero of circular scale division coincides with 25 divisions above the reference level. If screw gauge has a zero error of –0.004 cm, the correct diameter of the ball is
Answer & explanation
Correct answer: option 4
Diameter of the ball
= MSR + CSR × (Least count) – Zero error
= 5 mm + 25 × 0.001 cm – (–0.004) cm
= 0.5 cm + 25 × 0.001 cm – (–0.004) cm = 0.529 cm.