A single cell of e.m.f. 1.5 V is connected across a 0.30 resistor. The current in

A single cell of e.m.f. 1.5 V is connected across a 0.30 Ω resistor. The current in the circuit is 2.5 A.
a. Calculate the terminal p.d. and explain why it is not equal to the e.m.f. of the cell.
b. Show that the internal resistance r of the cell is 0.30 Ω.
c. It is suggested that the power dissipated in the external resistor is a maximum when its resistance R is equal to the internal resistance r of the cell.
i. Calculate the power dissipated when R = r.
ii. Show that the power dissipated when R = 0.50 Ω and R = 0.20 Ω is less than that dissipated when R = r, as the statement suggests.