JAMB - Physics (2000 - No. 19)
A radio is operated by eight cells each of e.m.f. 2.0V connected in series. If two of the cells are wrongly connected, the net e.m.f. of the radio is
8V
10V
12V
16V
คำอธิบาย
When cells are connected in series, their voltages add up. However, if two cells are connected in the wrong direction, they will subtract from the total e.m.f
If all cells were connected correctly, the total e.m.f. would be: Total E.M.F = 8 x 2.0V = 16V ( since no of cell = 8. and E.M.F of each cells = 2.0V)
When two cells are connected in the reverse direction, their contributions effectively subtract from the total e.m.f
Contribution from 2 wrongly connected cell = 2 x 2.0v = 4V
Therefore, Total E.M.F = 16 - 4 = 12V.