Having more turns in a transformer increases the magnetic flux DENSITY through the core.
The reason why using many coils in a transformer is more efficient, is that more turns will concentrate the magnetic field into the iron core better rather than having the magnetic flux go everywhere and anywhere, thus reducing the "iron loss" (the "iron loss" means whatever energy is lost in the iron core due to hysteria, eddy currents etc; whereas "copper loss" is loss due to heat dissipated in the wires). However if the number of turns are too numerous, there will be problems too because the iron core will be "saturated" (there is only so much magnetic flux that an iron core will be able to convey from primary to secondary windings, and if this is exceeded some of the input energy is wasted as heat).
Also increasing the number of turns of the coil means making the coil longer & increasing resistance, and therefore increasing the "copper loss", but this is usually quite small/insignificant compared to the "iron loss", so you can sort of ignore it.
There are actually some quite complicated equations that are used to determine at what number of turns the core is saturated (when a transformer operates at maximum efficiency the core must be ALMOST saturated), and this depends on a huge number of factors such as the permability of the core, voltage level, frequency etc, but you won't need to know these (unless you're doing EE at uni
).
In fact you won't really need to know more than half of what I posted, the main idea is just that moderation is needed. Not too much turns on the tranformer, but not too little either depending on the circumstances. In practice, it happens that the required number of turns is usually quite high, sometimes in the hundreds or thousands (or more!).
BTW kini, what's your dad's name? (the EE lecturer/academic staff at UNSW
)
