Combination Circuit Pickle

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Deleted member 350548

Joined Dec 31, 1969
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Hi all,

Another question form my paper i sat today, again I think this is very elementary but I am just slightly confused. Considering I want to continue in electrical engineering in the future i guess it's important I get things like this right. My question is to work out, I1, and i2, plus the voltage against the 3kOhm resistor. Now I am not sure I have obtained two values for i1, 2.5A and than for total 3.37mA. Not sure what is right, I understand essentially where I need to begin but lost along the way! -.-

Thanks allIMG_1316.JPG
 

AlbertHall

Joined Jun 4, 2014
12,385
You need to review the formula for resistors in parallel.
It is difficult to read for certain but it looks as if all the resistor values are in kilo-ohms. As a quick sanity check consider 1A flowing in a 1 kilo-ohm resistor needs a voltage of 1000V!
 

dl324

Joined Mar 30, 2015
17,001
Considering I want to continue in electrical engineering in the future i guess it's important I get things like this right.
Start by learning to keep multipliers straight. The resistors are in the K ohm range, so current will be in the mA range. I was taught to use capital letters for multipliers greater than 1 and small letters for multipliers less than 1; but K and k are both used for 1000.

My question is to work out, I1, and i2, plus the voltage against the 3kOhm resistor. Now I am not sure I have obtained two values for i1, 2.5A and than for total 3.37mA.
Units for I1 are wrong. 5V/2KΩ=2.5mA. How did you arrive at It=3.37mA? Correcting your units, you show I1=2.5mA and I2=1mA.

Your diagram for the voltage divider is wrong.
 

MrAl

Joined Jun 17, 2014
11,565
Hi,

Yes the resistor values look like they are in kilo ohms. Current will be 2.5/1000 then for i1.
 

WBahn

Joined Mar 31, 2012
30,243
Start by learning to keep multipliers straight. The resistors are in the K ohm range, so current will be in the mA range. I was taught to use capital letters for multipliers greater than 1 and small letters for multipliers less than 1; but K and k are both used for 1000.

Units for I1 are wrong. 5V/2KΩ=2.5mA. How did you arrive at It=3.37mA? Correcting your units, you show I1=2.5mA and I2=1mA.

Your diagram for the voltage divider is wrong.
People that use K for kilo are doing it wrong -- K is the SI unit for temperature, the Kelvin (though this along doesn't make it wrong since 'm' is used for both a scaling prefix and a dimensional unit). The prefix k is the one engineering scaling prefix (exponents that are multiples of three) that violates the upper/lower case 'rule', which is probably why you see it used incorrectly so often. The prefixes for 10 (da) and 100 (h) also violate it, but you very seldom see either (except for h in hectares)
 

MrAl

Joined Jun 17, 2014
11,565
People that use K for kilo are doing it wrong -- K is the SI unit for temperature, the Kelvin (though this along doesn't make it wrong since 'm' is used for both a scaling prefix and a dimensional unit). The prefix k is the one engineering scaling prefix (exponents that are multiples of three) that violates the upper/lower case 'rule', which is probably why you see it used incorrectly so often. The prefixes for 10 (da) and 100 (h) also violate it, but you very seldom see either (except for h in hectares)

Hi,

After some recent years i have come to appreciated the coding such as "2k2" instead of 2.2k. That seems to make it clear what it is. I guess 2k would have to be written "2k0" then. "2K2" might be ok then.
However, if we see 2K next to a resistor and nothing else, i dont think we would confuse it with temperature. Also, sometimes only upper case letters are supported in which case we would have no choice.
"NOW ENTER THE VALUE OF THE RESISTOR"
>>>> "2K"
 

ErnieM

Joined Apr 24, 2011
8,377
Anyone looking at a schematic diagram who sees a resistor marked something-K who thinks the K is for a temperature had better find a profession that does not involve electronics.
 

WBahn

Joined Mar 31, 2012
30,243
Anyone looking at a schematic diagram who sees a resistor marked something-K who thinks the K is for a temperature had better find a profession that does not involve electronics.
The fact that sloppy notation is not likely to be confused in a particular situation is hardly and excuse to use sloppy notation when there is no need to.
 

WBahn

Joined Mar 31, 2012
30,243
Hi,

After some recent years i have come to appreciated the coding such as "2k2" instead of 2.2k. That seems to make it clear what it is. I guess 2k would have to be written "2k0" then. "2K2" might be ok then.
However, if we see 2K next to a resistor and nothing else, i dont think we would confuse it with temperature. Also, sometimes only upper case letters are supported in which case we would have no choice.
"NOW ENTER THE VALUE OF THE RESISTOR"
>>>> "2K"
Are thee situations in which you can't use proper notation or in which an alternate notation has sufficient advantages to warrant its use even when proper notation could be used? Sure. Never even hinted that this wasn't the case.
 
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