# Calculating power with a wattmeter

Discussion in 'Homework Help' started by nyasha, Oct 15, 2011.

1. ### nyasha Thread Starter Active Member

Mar 23, 2009
90
1
I calculated the power for this circuit and got a positive value of 1100 watts. However in the textbook they have the solution being negative. Can someone please tell me why ?

2. ### #12 Expert

Nov 30, 2010
16,705
7,358
One point of view is that a negative amount of power means the circuit is absorbing 1100 watts of heat from the surrounding air. This being impossible, I thing the book is wrong. Typographical error.

3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
The winding for measuring the voltage (bottom one) has its dot to the right. This means that it measures a negative voltage (or 180 degrees phase shifted) which gives a negative power.

4. ### #12 Expert

Nov 30, 2010
16,705
7,358
I wish my electric company believed that!

5. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,403
1,227
Doesn't matter. They would use abs(#12's power meter) to compensate for the "negative power".

#12 likes this.