significant figures

[fahadii92]

Assalam O Alaikum!
why marking sceheme doesnot always give answer correct to lowest sig. fig. in the question(particularly in physics marking schemes) ... i have always seen a mixture.. what number of sig. fig. should be reasonable and is there any marks deduction for quoting wrong sig fig. or theres a range ?

 

[Casablanca]

Sig. fig. should be according to your raw data. For example, if your reading is 1.2cm, try to stick to 2 sig.figs. in all cases. In marking scheme, you're allowed one more, but to avoid complications, just stick to what is safe.

 

[fahadii92]

in 30 % cases i have seen raw data being in e.g 2 sig fig and answer given in 3? why is that

 

[Casablanca]

Because, like I said, you're allowed to add in one more sig. fig. for accuracy. Or maybe they want to keep it uniform. For example, if most readings are in 3, they might add a third s.f in ones which there are only 2.

For the sake of simplicity stick to 2, like I do. I always get good grades in practicals, and I always use minimum sig. fig. from raw data.