In many practical applications, we use variable electric current I(t), that is, the current that changes with time t. A couple of examples that we will consider in this problem: (a) Current I(t)=I0 cos(2πf·t) that oscillates with frequency f. (b) Current I(t)=I0 e−t/ that decays in time with time constant . Our questions will be related to the currents with amplitude I0=1.56 A running in the copper (resistivity = 1.7 10-8 Ω·m) wire of diameter d=3 mm and length l=0.56 m. For example (a), how much energy Wa is dissipated in the wire via Joule heating during one period of current oscillations for frequency f=50.4 Hz?: Wa= mJ. With the oscillating current, the amount of charge passing through any cross-section of the wire would, of course, also oscillate with the same frequency. What is the amplitude Q0 of charge oscillations?: