Question

The magnetic field observed at a point P at a distance of R from the straight current carrying conductor decreases as we decrease R. Why this happens.

Answer 1

i think your question is wrong magnetic field should increase as you take point closer(r decreases) to the wire carrying current. . .
\[B=\mu _{o} I /2\pi r\]
its formula of magnetic field on a point due to charge carrying straight wire. . .
thus
\[B \alpha 1/r\]
magnetic field is inversly proportional to R.

Answer 2

yeah, sorry. I meant to write increases. But what is the phenomenon which decreases it. I know increasing the current increases the number of charged particles in motion. But what does this decreasing the distance from the conductor wire increases the magnetic effect of the electromagnet.

Answer 3

see you have the formula and verbal reason is as you move away magnetic field line density would decrease so you will feel lesser magnetic field . . .