What is the difference between AC (alternating current) and DC (direct current) in terms of their flow of electric charge?

Engineer, During the transmission of electricity over long distances, an alternating current is passed over aluminium cables at high voltages and low current. .i) Give two reasons why is alternating current  (a.c) used in preference to direct current (d.c) ?. ii) Give two reasons why are aluminium cables preferred to copper for long distance transmission of electricity?

36. An intermittent and non-symmetrical alternating current like that obtained from the secondary winding of an induction coil

 In thermal electric generating plant, overall efficiency is improved when

a.  Boiler pressure is increased

b.  The difference between initial pressure and temperature and exhaust pressure and temperature are held at a maximum

c.  Load on the units is increased

d.  Increased the no. of generator