A student measures a length as 4.2 cm with a ruler that has markings every 1 mm. What is the uncertainty in the measurement?
A±1 mm
B±0.5 mm
C±1 cm
D±0.1 mm
Explanation
📌 The uncertainty is generally ±½ the smallest division of the measuring instrument. Ruler divisions are 1 mm, so uncertainty is about ±0.5 mm. Distractor A overestimates by 2×; C uses the wrong division (cm not mm); D underestimates the uncertainty (would need a much finer instrument).