Measuring length, time, mass, weight, volume and other simpler things are easy to understand and there are many ways to measure them.
Like i can use a meter scale, hand, and any other things to measure length and assignt to it any arbitary unit. And i know these ‘lengths’ are interconvertible. I have an intuitive idea what length is. But i cant understand how they measure charge or other things.
I want a detailed explanation of how temperature, charge, and electric current are measured.
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Charge is typically not directly measured, although you can do it (search keyword: gold leaf electrometer). In basic terms, there is a natural unit of charge: the charge on an electron. Because like charges attract and unlike charges repel, you can count a net imbalance of charges between two objects by observing the force one exerts on the other. The reason you find excuses to do anything else rather than measure charge because the experimental equipment is fiddly as hell.
*Current* is measurable quite easily via Ohm’s law: the voltage drop across a known resistance is equal to the product of the current through it and its electrical resistance. Or if you don’t have a calibrated voltmeter, you can use the fact that the current in a wire produces a magnetic field: pass your wire through a magnet and measure the force on it. The amp was defined until 2019 as the current that produces 0.2 micronewton of magnetic force between two long thin straight wires one metre apart in a vacuum.
(The amp is now defined as a current of 10¹⁹ electrons every 1.602176634 second. This is way harder to measure, but easier to define.)
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