Calculate the solid angle subtended by the periphery of an area of $1 \, cm^2$ at a point situated symmetrically at a distance of $5 \, cm$ from the area. (in $, sr$)

What is the uncertainty in time measured by a cesium atomic clock?

Define the unit of mass in nuclear physics. Explain the measurement of the mass of a body.

$1'' = \dots \text{rad}$

It is claimed that two cesium clocks,if allowed to run for $100$ years,free from any disturbance,may differ by only about $0.02\; s$. What does this imply for the accuracy of the standard cesium clock in measuring a time-interval of $1\; s$?

What is called a basis? What is parallax? Define angular diameter.