4: internal resistance

The difference between the p.d. Measured at the terminals of the power source (the terminal p.d.) and is less than the actual e.m.f

Lost volts

E.m.f = terminal p.d. + lost volts

Relationship b/W e.m.f. Terminal p.d. And lost volts

lost volts = I x r

where r is the internal resistance in ohms

equation for lost volts

emf > terminal p.d. (unless there is no current)

emf ___ terminal p.d.

E = V

when the current is very small

E = I(R+r)

derive the equation for emf

* connecting cells in series increases the available e.m.f. but also increases the internal resistance. this limits the current that the combination can produce
* the same two cells connected in parallel produce the same e.m.f as one cell but have a much smaller internal resistance so provide a greater current

does series or parallel produce more current and why

this allows them to be recharged using higher current without overheating or wasting a lot of energy, so that recharging is fast

why is low internal resistance used in car batteries and rechargeable batteries

this acts as a safety feature, preventing the power supply from delivering a fatal electric current

why is high internal resistance used in classrooms