The $P-V$ diagram of an ideal gas is as shown in the figure. The work done by the gas in the process $ABCD$ is:

$A$ stone tied to a string of length $L$ is whirled in a vertical circle,with the other end of the string at the center. At a certain instant of time,the stone is at its lowest position and has a speed $u$. The magnitude of the change in its velocity as it reaches a position where the string is horizontal is

The perimeter of a $\triangle ABC$ is $6$ times the arithmetic mean of the sine of its angles. If its side $BC$ is of unit length,then $\angle A=$

Assertion $(A)$: Rapidly changing temperatures can be measured by thermocouples. Reason $(R)$: The thermal capacity of the junction of a thermocouple is very small.

Which of the following is the correct sequence of the various steps of Herbarium formation?
$1$ Drying $2$ Poisoning $3$ Collection $4$ Labelling $5$ Mounting $6$ Deposition $7$ Stitching

What is the path difference for destructive interference?