13.4 More circuit calculations Flashcards
how do you calculate the current passing through the cell
calculate the total resistance using g resistor combination rules
remember to add on internal resistance of the cell if it isn’t negligible
cell current =
cell emf / total circuit resistance
how do you work out the current and pd for each resistor in series
start with the resistors in series with the cell which therefore pass the same current as the cell current
Pd across each resistor in series with the cell =
current x the resistance of each resistor
how do you work out the current and pd for each resistor in parallel
current through one resistor = pdparallel / resistor resistance
current through each resistor in parallel
pd across the parallel combination / resistors resistance
if cells are connected in the same direction what is the emf
the total emfs of each cell added together to find the net emf
what happens if the cells are connected in opposite direction to each other in the circuit
the net emf is the difference between the emts in each direction
what is the total internal resistance of 2 cells
the sum if the individual internal resistances
this is because the cells and therefore the internal resistances are in series
for a circuit with n identical cells in parallel the current through each cell =
=I/n where I is total current supplied by the cells
what is the lost pd in each cell for same cells in parallel
I/n r = ir/n
where r is the internal resistance of each cell
what is the terminal pd across each same cell in parallel
v = e - ir/n
what happens each time an electron passes through the cells in parallel
it travels through one of the cells only (as the cells are in parallel)
therefore the cells act as a source of emf e and internal resistance r/n
what do you assume that a diodes forward pd is
0.6 v whenever a current passes through it
what do you assume a silicon diodes resistance
it has infinite resistance in the reverse direction or at pds less than 0.6 v in the forward direction
therefore that do we assume about a circuit with one or more diodes
a pd of 0.6v exists across a diode that is forward based and passing a current
a diode that is reversed based has infinite resistance
what would happen if a diode was reversed
the circuit current would be 0 and so the pd across the resistor would be 0
