Really basic resistance question, but not sure.

Hey guys,

I feel like an idiot asking this, but if the question is talking about 1k7 ohms of resistance, am i to believe that is the same as 1700 ohms?

Thanks ^^

James

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stewartcs
Hey guys,

I feel like an idiot asking this, but if the question is talking about 1k7 ohms of resistance, am i to believe that is the same as 1700 ohms?

Thanks ^^

James
Yes.

CS

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What is this notation?

stewartcs
What is this notation?
I think its crap. Doesn't really make sense to me, but I've seen it on spec sheets before (then they put = 1700 ohms beside it in parenthesis).

CS

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I think its crap. Doesn't really make sense to me, but I've seen it on spec sheets before (then they put = 1700 ohms beside it in parenthesis).

CS
From what you say, I presume it's done by engineers?

berkeman
Mentor
Dunno if it's crap, but you do see it in various places, so it's good to be familiar with it.

1k7 = 1.7k Ohms

1r7 = 1.7 Ohms

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Just one more question. You both say this is seen in various places, like spec sheets. Where else?

stewartcs
1r7 = 1.7 Ohms
That's a new one I haven't seen.

I suppose it may be to standardize the use of a comma (in Europe and other places) and a decimal in the US.

i.e. 1,7KOhms compared to 1.7KOhms.

berkeman
Mentor
Just one more question. You both say this is seen in various places, like spec sheets. Where else?
It's common on European schematics. Either in application notes, or in customer schematics (in my work, I help out with customer design reviews fairly often, so I see a lot of schematics from all over the world).

Also, you'll sometimes see medium-size power resistors labeled with the 2R2 type of notation, if the value is written on the resistor (as opposed to using colored bands).

ranger
Gold Member
Isn't it also possible for that notation to represent a potentiometer? I could swear that I've built circuits using 4k7 pots.

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Isn't it also possible for that notation to represent a potentiometer? I could swear that I've built circuits using 4k7 pots.
And that would mean...?

I've seen the notation on the resistors themselves before.

f95toli
Gold Member
Isn't it also possible for that notation to represent a potentiometer? I could swear that I've built circuits using 4k7 pots.
Which simply means a potentiometer with a maximum resistance of 4k7, i.e. 4700 Ohms

This notation is very common and often very conventient; especially when you have small letters on a component since you do not have to use a point since e.g. 1.7k can easily be misstaken for 17k. 1k7 and 17k look very different.

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> 1k7 = 1.7k Ohms

> 1r7 = 1.7 Ohms

The k I've understood, but what is the 'r'? What would be 720 in this notation? (I don't know what they use for 100. But, suppose they use h, then it'll be 7h2, right)

berkeman
Mentor
> 1k7 = 1.7k Ohms

> 1r7 = 1.7 Ohms

The k I've understood, but what is the 'r'? What would be 720 in this notation? (I don't know what they use for 100. But, suppose they use h, then it'll be 7h2, right)
I belive the R is just to show it is a resistor.

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I belive the R is just to show it is a resistor.
And the 'k'?

berkeman
Mentor
And the 'k'?
Kilo = 1000

Since there is no prefix for unity, they apparently picked the "R" for the resistor decimal point designator.

You will also see 47R for 47 Ohms, BTW.

The electronics use k with the meaning Kohm, not k as 1000x. It's just a coincidence. They never use h or d to mean x100 or x10.
Resistors of several kilo ohm to a hundred kohm are very common, so they just say 2.2 k or 2k2, 100k etc.
They also use r as ohm, just because in electronic circuit schematics, resistors are often noted as R1, R2 etc...

berkeman
Mentor
The electronics use k with the meaning Kohm, not k as 1000x. It's just a coincidence.
Why do you think it's a coincidence that the prefix k is used for kOhm? How many Ohms in a kOhm?

Why do you think it's a coincidence that the prefix k is used for kOhm? How many Ohms in a kOhm?
If not, they should use k, h, d as well. But i have never heard. I use to spend some time working with electronics circuits , electronics devices and the like, and we used the word k so often that we never thought it's x1000 (in fact it is), I just thought kohm is a unit which is used as often as ohm (even more).

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Refer to my question in post #5. It's a wonder I'm writing this and you are reading this.

(Oops, esteemed berkeman (a mentor in engineering) is on this thread! Didn't notice... )

berkeman
Mentor
If not, they should use k, h, d as well. But i have never heard. I use to spend some time working with electronics circuits , electronics devices and the like, and we used the word k so often that we never thought it's x1000 (in fact it is), I just thought kohm is a unit which is used as often as ohm (even more).
Nope, definitely not a coincidence. In electronics, we use MKS and the associated prefixes:

http://en.wikipedia.org/wiki/SI_prefix

Just as km = 1000m, kOhm = 1000 Ohms. Same deal.

It is also true that in engineering, we tend to stick with the prefixes that are powers of 3:

M = 10^6
k = 10^3
m =10^-3
$$\mu$$ = 10^-6
etc.

Like, if you turn on "Engineering Notation" on an HP calculator, you get scientific notation, but snapped to the nearest 3-power.

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OK, now I feel a bit reassured with the explanations.

Sure that K, M are x10e3 and x10e6. But if you use that unit very often, the original meaning fades away. It's just like when you read some capacitors: muy, n, p. No one thought they are of one millionth or one billionth of a farad.

berkeman
Mentor
Sure that K, M are x10e3 and x10e6. But if you use that unit very often, the original meaning fades away. It's just like when you read some capacitors: muy, n, p. No one thought they are of one millionth or one billionth of a farad.
I disagree. We do math with those numbers all the time, often in our head. How can you calculate the LPF pole from R and C numbers, and not do the math on the prefixes too? The meaning of numerical prefixes never fades away -- they are part of the number itself.