6.19 Turns

Recall and use the relationship between input (primary) and output (secondary) voltages and the turn ratio for a transformer:

The ratio between voltage and turns is shown above, this can be used to predict the output voltage of a transformer. It is worth noting that that because this is a ratio you could place the secondary turns and voltage on top as long as both are on the top or bottom (i.e. Vp and Ns on top would be incorrect)

Example question:

a) This is a step-up transformer because the voltage is being decreased

b)

        

     

        

        

c)

     
 
 
d) 24 Watts of Power is delivered to the lamp [assuming 100% efficiency]
e) 24 Watts [see 6.20]
f)
    

 
 
g) If the transformer is only 50% efficient, half of the energy would be wasted. In order to retain 24Watts of power the primary current must be doubled so that the primary power is 48Watts.