Question

why do we have different units for the same physical quantity?? ​

Answer 1

Answer:

Sometimes they sound different but are identical. Like 1 joule/second = 1 watt or 1 Newton/Coulomb = 1 Volt/metre.

Other times they are just multiples to make the unit more convenient to use. You would probably mot want to measure how much salt to add to some dough when making bread in kilograms, grams seem to be more appropriate. If I looked up the length of the river Nile, I would not really want to know the answer in centimetres.

Using prefixed like mega, kilo, milli, nao etc we can make our unit much bigger or smaller and so more convenient.

There is another form of convenience where the multipliers are not simple multiples of 10. Particle Physicist accelerate particles in a particle accelerator believe it or not! The tend to use the unit of energy of the ‘electron volt’. This is the energy a particle with a single charge gains when it is accelerated through a potential difference of 1 volt. It is a small unit of energy but this is suitable for atoms and sub atomic particles. They may make the unit bigger by using kilo, Mega, Giga etc.

They could use joules and the conversion is simple enough:

1 eV = 1 x 1.6X10^-19 joules. The conversion factor is 1.6x 10^-19 which is the size of the charge on an electron measured in Coulombs. The particle physicists never really use joules so rather than endless multiplying by the conversion factor ( and the later on dividing by it again) they simply don’t bother. The stick to using eV or some bigger version like MeV.

Explanation:

Answer 2

Answer:

the units we use to measure should be considerably be proper to what we want to measure.....this is because if you want to measure the length of you eraser u use cm......in case of your pencil box u use inches........but these cannot be used to measure the distance between two cities or states. So you see that it entirely depends on what we want to measure that we use different units for the same physical quantity because al....cm, inches and even km are used for distance measurements