Why in electronics we sometimes require high voltage and low current ?

Ans: Basically when we talk about power transmission (P=V*I) . there we need to avoid any wastage of power during transmission from transmission line. So , in that case from plant (power plant) we send power in such a way that its voltage gets high and current gets small. Now By doing this :-

1) due to low current we don't require that thick wires. (Not only this in case we use thick wire there will be overheating due to joule heating effect)

2) due to low current we can able to avoid wastage in transmission line ! But How ? for that you have to consider an example : Let in your home you need 10V & 10A to run a particular device i.e (P= 10V * 10A=100W ). and for a case consider Plant is providing you 10V & 10 A (P=10V*10V=100W) through a transmission line having 10 ohm resistance. in this case on the transmission line there is a voltage drop of (V=I*R=10A*10ohm=100V) .Now this means you needed

--> 100V( power loss in transmission line) + 10 V( that you need to run your device) =110 V

which means  extra power needed by  plant to compensate transmission losses = 100V *10A=1000W .i.e plant needs 1000W extra in addition to your 100W that you needed in your home. Now think in case if you transmitted 0.1A and 1000V sets of value from power plant (i.e low current high voltage) to your home via same transmission line having 10 ohm resistance. This time you will achive same power P=0.1A*1000V=100W but this time your power loss will be just

V=10ohm*0.1A=1V     =>  P=1V * 0.1A=0.1W .

now judge yourself don't keep high difference between voltage and current (keeping current very small) and bear high loss in power and some high drops of voltages in transmission line or maintain a huge difference between them (keeping current very small) and compensate negligible losses.

The whole above scenario maintains a low V1⋅I1=V2⋅I2=const.

The show below is the general Power transmission model

And in India we follow Power transmission Model as shown below

Now I will not stop here i am little more curious don't u wonder

How that huge voltage(Pump) of 1000V cause small current(speed of electron) of 0.1 A .How is it even possible ?

Ans For that you have to understand the coiling mechanism of transformer.it is like that if you have more number of turns of coil as compared to input turns.then your transformer will act like step up  transformer and if less number of turns at output as compared to input then your transformer will act as a step down transformer. Beside coiling mechanism if you make out more physics behind it then u will probably got more satisfactory answer.

Watch The Video Shown Below