Why I*ε Cannot be Used to Calculate Power

[hidemi]

Homework Statement

In a series RLC circuit the rms value of the generator emf is ε and the rms value of the current is i. The current lags the emf by Φ, The average power suppplied by the generator is given by:

A. (iε/2) cos Φ
B. iε
C. i^2/Z
D.( i^2)Z
E. (i^2)R

ans: E

Relevant Equations

P = IV = I^2R = V^2/R

Why can't we calculate use I*ε to obtain the power?

 

[Keith_McClary]

If it is a pure LC circuit (R=0) (or pure L or pure C) there will be no energy/power absorbed.

 

[hidemi]

If it is a pure LC circuit (R=0) (or pure L or pure C) there will be no energy/power absorbed.

I think I got what you mean, but I would like to double check.
Is it because inductor and capacitor both can store energy while resistance only dissipates energy, and thus resistance is the only electric accessory that can generate power?

 

[Keith_McClary]

@hidemi Right.

 

[hidemi]

@hidemi Right.

Thank you for confirming!