The reading of the ammeter in the circuit shown will be: (in $A$)

Two particles $P$ and $Q$ start from the origin and execute simple harmonic motion along the $X$-axis with the same amplitude but with periods $3 \ s$ and $6 \ s$,respectively. The ratio of the velocities of $P$ and $Q$ when they meet is

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

The collector plate in an experiment on the photoelectric effect is kept vertically above the emitter plate. $A$ light source is turned on,and a saturation photocurrent is recorded. An electric field is then switched on,which has a vertically downward direction.

Which of the following oxides of nitrogen is a blue solid?

Apart from tetrahedral geometry,another possible geometry for $CH_4$ is square planar with the four $H$ atoms at the corners of the square and the $C$ atom at its centre. Explain why $CH_4$ is not square planar?