physics chapter 13.3 + 13.4 emf, internal resistance, + circuit calculations

what is the internal resistance of a source of electricity due to

opposition to the flow of charge through the source, which causes electrical energy produced by the source to be dissipated inside the source when charge flows through it

the electromotive force of a source

the electrical energy per unit charge produced by the source

equation for emf, in terms of energy and charge

emf = E/Q

the pd across the terminals of a source

the electrical energy per unit charge delivered by the source when it is in a circuit

the internal resistance of a source

the loss of potential difference per unit current in the source when current passes through the source

difference between the terminal pf and the emf in a circuit whenever current passes through the source

the terminal pd is less than the emf whenever current passes through the source - due to the internal resistance of the source

the lost pd inside a cell

the pd across the internal resistance of the cell - equal to the difference between the cell emf and the pd across its terminals

the lost pd, in terms of energy

the energy per coulomb dissipated or wasted inside the cell due to its internal resistance

equation for emf, in terms of current, external resistance, and internal resistance

emf = IR + Ir

what is the power supplied by the cell equal too

the power delivered to the external resistance + the power wasted in the cell due to its internal resistance

equation for power supplied by the cell

I x (emf) = I^2R + I^2r

when is the maximum power delivered to the load when a source delivers power to a load

when the load resistance is equal to the internal resistance of the source

how can pd across the terminals of a cell be measured when the cell is in a circuit

by connecting a high-resistance voltmeter directly across the terminals of the cell

relationship between terminal pd and current

the terminal pd decreases as the current increases - because the lost pd increases as the current increases

what is the terminal pd equal to at zero current

the cell emf - because the lost pd is zero at zero current

shape of the graph for terminal pd against current

a straight line, with a gradient = -r, and a y-intercept = emf

rearranged equation for a graph of terminal pd against current

IR = -Ir + emf

equation for current passing through a cell

cell emf / total circuit resistance

equation for pd across each resistor in series with the cell

current x resistance of each resistor

equation for pd across parallel resistors

combined resistance x the cell current

equation for current through each resistor when resistors are in parallel

pf across the parallel combination / resistor's resistance

equation for current through the cells for cells in series

overall (net) emf / total resistance

net emf for cells connected in the same direction in series in a circuit

the sum of the individual emfs

net emf for cells connected in opposite directions to each other in series in a circuit

the difference between the emfs in each direction

the total internal resistance in a circuit, when the cells are in series

the sum of the individual internal resistances - because the internal resistances are in series since the cells are in series

equation for current through each cell for n identical cells in parallel

total current supplied by the cells / number of identical cells in parallel - I/n

equation for lost pd in each cell for n identical cells in parallel

(I/n) x r = (Ir)/n

why do cells in parallel act as a source of emf and internal resistance

because each time an electron passes through the cells, it travels through one of the cells only

forward pf of a silicon diode

0.6V

when is the resistance of a silicon diode infinite

in the reverse direction, or at pds less than 0.6V in the forward direction

Kirchoff's first law

at any junction in a circuit, the total current entering the junction is equal to the total current leaving the junction

Kirchoff's Second Law

for any complete loop in a circuit, the sum of the emfs around the loop is equal to the sum of the potential drops around the loop