@HarjotDhillon It is just a convention. It's easier to picture something varying by ±90° because this is a relatively small change. By contrast moving by 270° means moving ³⁄₄ of a wavelength.

@JohnRennie possible explanation that I thought was that voltage come in circuit before current starts flowing. Time gap is small (just microseconds) but not exactly zero. Maybe that's why we take voltage as reference point.

I don't think that's the reason.

I think it is just that 90° is easier to imagine than 270°.

So it's all just convention like : " I am not 1 hour late, I am 23 hours early."

Yes :-)

Ok thanks for your time.

toppr.com/ask/question/…

Shouldn't we hear beat of every combination. So we would hear 4 beats per second

desmos.com/calculator/bx55a9fnu7

I tried making graph but still same result : 2 beats