## rkparth5770 3 years ago A dimensionless quantity (a) never has a unit, (b) always has a unit, (c) may have a unit, (d) does not exist.

I had one of those once, and it did not have a unit.

2. rkparth5770

What was it then?

What is the unit of Pi?

4. rkparth5770

No unit

5. myko

what a unit of 25ºC

The unit is Celcius degree @myko

Can be converted to Fahrenheit units by a sharp student.

8. myko

so the answer is (c) may have a unit. Other definition for dimensionless quantity is scalar quantity

9. rkparth5770

Yeah But give an example with a unit and without a unit!

10. myko

i just did. And @radar gave with no units

11. myko

@radar also can convert it to Fahrenheit if you whant

12. rkparth5770

I need Examples One is temperature with a UNiT! So without unit?

In my humble opinion, the best answer would be "a"

14. rkparth5770

ohh why!?

Pi has no unit, just a value and an irrational value at that.

16. myko
17. rkparth5770

So why is it not unitless?

Plancks constant is just a value, no unit, it is just used to convert things that have a dimehnsion, ft, in. grams, degrees, lbs, etc. these are dimensionsal units.

19. rkparth5770

oh yes!

Review that link provided by @rkparth5770 and make a decision.

21. rkparth5770

What?! i did not provide any

Thanks @rkparth5770 for providing additional info on this "dimensionless" subject.

23. rkparth5770

24. Callisto

Hmmm... in my physics book, Planck's constant is 6.626...x10^(-34) Js , which is with a unit :S

Just picked that out of the dark @Callisto, didn't realize that Plalnck's constant was in some kind of unit. Should of stuck with Pi lol.

26. UnkleRhaukus

in SI units planks constant certainly does have dimensions, , that is why Max Plank devise his own set of units that made it, along with other constants like the gravitational constant and the speed of light dimensionless. i dont like the wording of the options, i would phrase the answer as " a dimensionless quantities has units that cancel out" for example $\pi=\frac{C[{l}]}{d[l]}=\frac{C[\text{cm}]}{d[\text{cm}]}=\frac{C\cancel{[\text{cm}]}}{d\cancel{[\text{cm}]}}=\frac{C}{d}$

Yes indeed Plancks constant does have units. I looked up (Google): Planck's constant = 6.626068 × 10^-34 m^2 kg / s Thanks UnkleRhaukus for the review.

Yes indeed Plancks constant does have units. I looked up (Google): Planck's constant = 6.626068 × 10^-34 m^2 kg / s Thanks UnkleRhaukus for the review.