《电路》（英文版）12-4 Use of the wattmeter

812-4 Use of the wattmeter NP=I‖I|cos(v.-v:) If a positive current is flowing into the(+)end of the current coil while the (+ terminal of the voltage coil is positive with respect to the unmarked end, an upscale reading is obtained

§12-4 Use of the wattmeter  W •  I − + • V N If a positive current is flowing into the (+) end of the current coil while the (+) terminal of the voltage coil is positive with respect to the unmarked end, an upscale reading is obtained. =| || | cos( • − • ) • • V I P V I  

10 10 v1=10020V V2=100∠00V 10I1+j5(11-)=j00 10+j5(1-1)=-100 1118∠153.4°4 P=V2Icos(0-1534°)=100×118×c0s153.4°=-1000( downscale) Reverse a coil(the voltage coil)

    + − = − + − = • • • • • • 10 5( ) 100 10 5( ) 100 1 1 1 I j I I I j I I j I A  = 11.18153.4 • cos(0 153.4 ) 100 11.18 cos153.4 1000 ( ) 2 P =V I − =   = − W downscale   [Reverse a coil(the voltage coil)] I 1 • V2 100 0 V  =  • V1 100 90 V  =  • − + 10 10 j5 • I − +  W  • I