An anemometer is the instrument commonly used to measure wind speed.
292
A spherometer has 250 equal divisions marked along the periphery of its disc and one full rotation of the disc advances the main scale by 0.0625 cm. The least count of the system is
Least count = main scale advance / number of divisions = 0.0625 cm / 250 = 0.00025 cm = 2.5×10^-4 cm.
293
One kilogram is actually mass of platinum-iridium alloy cylinder kept at International Bureau of Weights and Measures in France. The ratio of platinum and iridium is:
The international prototype kilogram was made from a platinum–iridium alloy of 90% platinum and 10% iridium.
294
In an experiment the angles are required to be measured using an instrument. 29 divisions of the main scale exactly coincide with 30 divisions of the vernier scale. If the smallest division of the main scale is half-degree (=0.5°), then the least count of the instrument is
For a quantity raised to the nth power, its percentage uncertainty is multiplied by n (the power factor).
299
The following observations were taken for determining surface tension of water by capillary tube method: Diameter of capillary, D = 1.25 × 10⁻² m and rise of water in capillary, h = 1.45 × 10⁻² m. Taking g = 9.80 m s⁻² and using the relation T = (r g h / 2) × 10³ N m⁻¹, what is the possible error in surface tension T?
Percent errors combine from D, h and g giving 0.8%+0.1%+0.7% = 1.6% total percentage error.
300
While measuring acceleration due to gravity by a simple pendulum, a student makes a possible error of 1% in the length of the pendulum and a negative error of 3% in the value of the time period. His percentage error in the measurement of the value of g by the relation g = 4π² (L / T²) will be
