NCERT Solutions for Chapter: Units and Measurement, Exercise 4: SA

Which of the following time measuring devices is most precise?

Give reason for your answer.

Give an example of a physical quantity which has a unit but no dimensions.

Give an example of a physical quantity which has neither unit nor dimension.

Give an example of a constant which has a unit.

Give an example of a constant which has no unit

Calculate the length of the arc of a circle of radius $31.0 \mathrm{cm}$ which subtends an angle of $\frac{\mathrm{\pi }}{6}$ at the center.

Calculate the solid angle subtended by the periphery of an area $1{\mathrm{cm}}^2$ at a point situated symmetrically at a distance of $5\mathrm{cm}$ from the area.

Time for $20$ oscillations of a pendulum is measured as $t_1=39.6 \mathrm{s}$; $t_2=39.9 \mathrm{s}$; $t_3=39.5 \mathrm{s}$; What is the precision in the measurements? What is the accuracy of measurement?