Determining the polarity of mutually inducted voltages using the dot convention

[stobbz]

Homework Statement

Determine the polarity of the induced voltages in L1 and L2.
[PLAIN]http://img406.imageshack.us/img406/730/31761140.jpg

According to the dot convention rule, when current enters the dotted terminal of a coil,the polarity of the voltage it induces in the other coil is positive at its dotted terminal.

And vice-versa, when current leaves the dotted terminal of a coil, the polarity of the voltage it induces in the other coil is negative at its dotted terminal.

The answer states that the mutually induced voltage in L1 is negative and that in L2 it is positive.

Homework Equations

N/A

The Attempt at a Solution

It seems a very simple question but I can't arrive to any other answer other than both mutually induced voltages being negative.

I've searched extensively to try and figure out where my misunderstanding lies, but no luck.

All help appreciated!

 

[Zryn]

According to the dot convention rule, when current enters the dotted terminal of a coil,the polarity of the voltage it induces in the other coil is positive at its dotted terminal.

Looking at L1, where does the current enter (dot or no dot?) and exit (dot or no dot?) the coil What does this mean for L2?

Looking at L2, where does the current enter (dot or no dot?) and exit (dot or no dot?) the coil What does this mean for L1?

 

[stobbz]

Looking at L1, where does the current enter (dot or no dot?) and exit (dot or no dot?) the coil What does this mean for L2?

Looking at L2, where does the current enter (dot or no dot?) and exit (dot or no dot?) the coil What does this mean for L1?

The current enters the dotted terminal of L1. My understanding is, that means a positive voltage will be induced at the dotted terminal of L2.

Going round the circuit in the direction of the current, wouldn't this produce a voltage rise across L2 (from undotted to dotted terminal)? In other circuits of this type, usually involving meshes, I have been adding voltage drops and subtracting voltage rises. Wouldn't a voltage rise be considered negative here?(May be where I am going wrong?)

At L2, the current enters the undotted terminal, so a negative voltage will be induced at the dotted terminal of L1. To me, this would signify another voltage rise, this time across L1 (from dotted terminal to undotted).

Thanks for replying.

 

[Zryn]

Yes you're exactly right, given your justification.

I believe however, that the question is looking for the voltages induced w.r.t. the dot's, rather than w.r.t. the circuit.

This may be an ambiguity worthy of clarification with your professor or whomever marks your papers.

 

[stobbz]

Good to know I'm not too far off the mark, thanks a lot for the clarification Zryn.