Question

what isproportionality sign,Why and when proportionality sign is used??

Answer 1

∝,this is the sign for proportionality.
This sign is used when two things directly or inversly related to each other.
Means,In ohm 's law ,
V = I×R
So from this relation we can say that V and I is directly proportional to each.If we increase the value of I then V will also increases.
We can write it as
V ∝ I.

To show relation between two quantities,we use this sign.