Page error

Novatek

Joined Jan 8, 2006
1
In vol1_1 in chpt_6 (www.allaboutcircuits.com/vol1_1/chpt_6/3.html) half way down the page you define the current devider rule as In=Itot*Rtot/Rn. When I tried to use it, it didn't work, so I looked at it closely because something didn't seem right from my electronics classes ( 12 years ago) so I traded the places of Rtot and Rn and everything worked fine from there on out.

Just thought you might like to know.

By the way, I really like your site, it is helping me to teach my wife electronics.

Novatek

Dcrunkilton

Joined Jul 31, 2004
422
Originally posted by Novatek@Jan 8 2006, 07:33 AM
In vol1_1 in chpt_6 (www.allaboutcircuits.com/vol1_1/chpt_6/3.html) half way down the page you define the current devider rule as In=Itot*Rtot/Rn. When I tried to use it, it didn't work, so I looked at it closely because something didn't seem right from my electronics classes ( 12 years ago) so I traded the places of Rtot and Rn and everything worked fine from there on out.

Just thought you might like to know.

By the way, I really like your site, it is helping me to teach my wife electronics.

Novatek
[post=12953]Quoted post[/post]​
You are correct if you remember the current through a resistor of a two resistor parallel network is the total current times the ratio of the other resistor over the sum of the other two. I show this in figure 1.
If you assume Rtotal is the sum of the two you are correct. You are doing pretty good to remember it from that long ago. It is one of the more obscure formulas.
[attachmentid=1094]

Toney's idea of Rtotal is the parallel resistance rather than the sum of the two. His formula is more general for more than two resistors. His formula is correct if Rtotal is the parallel resistance. I show this in figure 2 . If I substitute the product over the sum formula for parallel resistors I get the same more familiar formula of the other resistor over the sum of the two.
[attachmentid=1095]

The formula in the book is correct if you use the parallel resistance for Rtotal. The book -- web site has a less common formulation for a more general case , more than two resistors. Yeah, even I remember the other simple formula for two resistors. So I had to work through it to verify that it is correct.

A some point in the future, I may also include the simpler more familiar formulation. with R1+ R2 in the denominator. Though, this is not an outright error, it is certainly a point of confusion. Thanks for your input.