Question

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

Answer 1

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

Answer 2

What was it then?

Answer 3

What is the unit of Pi?

Answer 4

No unit

Answer 5

what a unit of 25ºC

Answer 6

The unit is Celcius degree @myko

Answer 7

Can be converted to Fahrenheit units by a sharp student.

Answer 8

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

Answer 9

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

Answer 10

i just did. And @radar gave with no units

Answer 11

@radar also can convert it to Fahrenheit if you whant

Answer 12

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

Answer 13

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

Answer 14

ohh why!?

Answer 15

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

Answer 16

I desagree:
http://en.wikipedia.org/wiki/Dimensionless_quantity

Answer 17

So why is it not unitless?

Answer 18

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.

Answer 19

oh yes!

Answer 20

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

Answer 21

What?!
i did not provide any

Answer 22

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

Answer 23

Welcum @radar

Answer 24

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

Answer 25

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.

Answer 26

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

\[\pi=\frac{C[{l}]}{d[l]}=\frac{C[\text{cm}]}{d[\text{cm}]}=\frac{C\cancel{[\text{cm}]}}{d\cancel{[\text{cm}]}}=\frac{C}{d}\]

Answer 27

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.

Answer 28

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.

Answer 29

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.