A transformer is used to transform AC voltage up or down.

A transformer which transforms voltage up is called a step up  

transformer



A transformer which transforms voltage down is celled a step
down transformer.

A transformer consists of 2 coils of wire wrapped around
an iron core.The voltage change depends on the number of
coils in each coil. If there are more turns of wire in the secondary
coil than the   primary coil the voltage is stepped up.
If there are less turns of wire in the secondary coil the
voltage is stepped down. The ratio of the turns in each
coil is the same as the ratio of the voltage.
 

   Turns primary          =   voltage primary
 Turns secondary            voltage secondary

Questions

1,A transformer has a primary coil with 100 turns and a        
   secondary coil of 500 turns
a,  Is it a step up or step down transformer?


b, If the voltage in the primary coil is 12 volts.
What is the voltage in the secondary coil?



2 A transformer steps down the voltage in a circuit from
240 volts to 12 volts. If there are 1000 turns in the primary
coil how many are there in the secondary coil?



3 Describe three situations where a step down transformer is used
and one situation where a step up transformer is used.