# Instantaneous power

#### jonjkj

Joined Feb 15, 2008
4
Course question asks; what is the instantaneous power in watts if a circuit has 60 electrical time degrees and an instantaneous voltage of 122.5? Question is straight out of TVPPA course work.

#### Papabravo

Joined Feb 24, 2006
13,923
Your question, as stated, is meaningless. A circuit cannot have 60 time degrees. Please rephrase the question.

#### jonjkj

Joined Feb 15, 2008
4
I think the question was poorly stated also, but it would appear to me that at 60 degrees 122.5 volts the current would be .707 amps which would put the power at 86.6 watts, or am I way off again?

#### JoeJester

Joined Apr 26, 2005
4,259
does that book have other "examples" from which you can tap the knowledge well?

#### Papabravo

Joined Feb 24, 2006
13,923
I think the question was poorly stated also, but it would appear to me that at 60 degrees 122.5 volts the current would be .707 amps which would put the power at 86.6 watts, or am I way off again?
Well I for one don't see how you came to that conclusion. We do not know what the phase relationsip between the cirrent and voltage wave forms are. We do not know the peak value of either the current or the voltage waveform. Heck we don't even know if they are sinusoidal! We need to know what 60 degrees refers to.

BTW
sin 45 = cos 45 = SQRT(2)/2 = 0.707.
AND cos 60 = 1/2 = 0.5 and sin 60 = SQRT(3)/2 = 0.866

just in case you had forgotten these little pearls.