What is $1$ radian ? What is $1$ steradian ?
$(1)$ Plane angle subtended at centre by arc of circle having length equal to radius is called radian.
$(2)$ Angle subtended on $1 \mathrm{~m}^{2}$ area on sphere of $1 \mathrm{~m}$ radius is called 1 steradian.
Unit of energy in $SI$ system is
Which of the following is a derived unit
Newton-second is the unit of
A suitable unit for gravitational constant is
$'Torr'$ is the unit of