A source of emf E = 15 V and having negligible internal resistance is connected to a variable resistance, so that the current in the circuit increases with time as i = 1.2 t + 3. Then, the total charge that will flow in first five second will be:

10 C 20 C 30 C 40 C

30 C

q = $\int\limits_0^5 idt=\int\limits_0^5(1.2 t+3) dt$ = 30 C