# resistor question?

Discussion in 'General Electronics Discussion' started by subplay, Jul 2, 2013.

1. ### subplay

17
0
Jun 2, 2013
Hi I have a schematic im rebuilding. on the diagram, the resisitors feeding the leds are 330 ohm. But in there there is one resistore the says 3.3m

Thanks again all

2. ### subplay

17
0
Jun 2, 2013
Whats a 3.3m resistor?

Hi all im making a circuit of a schematic, I need 10 330ohm resistors, but 1 x 3.3m

Can anyone clarify what that is? and is there a link where I could pick up one from...

or is the 3.3m another way of saying 330 ohms?

Thanks

3. ### davennModerator

13,833
1,950
Sep 5, 2009
hi
is it really shown as 3.3m or is it really shown as 3.3M or 3M3 ?

3.3M or 3M3 = 3.3 MegaOhms ( they don't make 3.3 milliOhm resistors as far as I'm aware)

Upper and lower case lettering is extremely important to get correct in electronics and physics in general

and Mr Ohm would prefer you capitalise his surname

lower case m = milli (1/1000th) upper case M = million

Dave

Last edited: Jul 3, 2013
4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,496
2,837
Jan 21, 2010
That is either 3.3M (3,300,000 Ohms) or 3.3m (0.0033 Ohms).

Can you check whether it's "m" or "M", and even better, show us the schematic.

A 3.3m resistor would typically be in series with a high current load (say between 30 and 200A) or as a shunt for a current meter (effectively the same).

A 3.3M resistor is a very high value and would be (perhaps) in a timing circuit, or other places with very low currents.

Last edited: Jul 3, 2013
5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,496
2,837
Jan 21, 2010
Subplay, can you see why we get annoyed by people starting multiple threads for exactly the same topic?

6. ### duke37

5,364
771
Jan 9, 2011
There are several places to get components in the UK. I get my bits from R.F Potts of Derby. Most big towns have a Maplins. RS components, Farnell, Cricklewood, Bowood are alternatives to get them by post.

7. ### KrisBlueNZSadly passed away in 2015

8,393
1,271
Nov 28, 2011
Ohm should not be spelled with an initial capital unless you are specifically talking about Mr. Georg Simon Ohm, or his Law. It's correct to say that a resistor value is 10 ohms (without the capital O).

When a unit is written as a single letter, the capital is used; for example, 10 µF (microfarads). There are exceptions: seconds should always use the lower-case letter: ps, ns, µs, ms, s, to distinguish them from siemens, the unit of conductance, which uses the upper-case letter. Times written with units of "µS" and "mS" are often seen, but are wrong.

The SI units for resistance should be written milliohm, ohm, kilohm (not kiloohm or kilo-ohm) and megohm (not megaohm or mega-ohm).

Other units that are named after people follow the same pattern:

microvolt, millivolt, volt, kilovolt, megavolt (named after Alessandro Volta);

nanoamp, microamp, milliamp, amp (named after Ampere);

nanohenry, microhenry, millihenry, henry (named after Joseph Henry) (There doesn't seem to be a consensus on whether the plurals should be written microhenrys, etc, or microhenries, etc.)

8. ### davennModerator

13,833
1,950
Sep 5, 2009
I could agree except where there is a prefix else its a capital

Henry etc

SI units

Base units: *Ampere ·*Candela ·*Kelvin ·*Kilogram ·*Metre ·*Mole ·*Second

Derived units: *Becquerel ·*Coulomb ·*Degree Celsius ·*Farad ·*Gray ·*Henry ·*Hertz ·*Joule ·*Katal ·*Lumen ·*Lux ·*Newton ·*Ohm ·*Pascal ·*Radian ·*Siemens ·*Sievert ·*Steradian ·*Tesla ·*Volt ·*Watt ·*Weber

Dave

9. ### Miguel Lopez

252
63
Jan 25, 2012
Units are only represented with capital letters symbols when they are derived from a person's name.

second, meter, mol, candela, radian....etc should always be represented as symbols using non-capital letters.

The only exception that I now remember is litre, which can be represented with a capital "L" to diferentiate it from the symbol for length "l" or from the number "1"

10. ### KrisBlueNZSadly passed away in 2015

8,393
1,271
Nov 28, 2011
Thanks Miguel for the clarification.