19. At relatively light load, transformer efficiency is low because-
A. transformer losses are high
B. secondary output is low
C. fixed loss is high in proportion to the output
D. Cu loss is small
When a transformer designed to increase voltage from primary to secondary called step-up transformer and when it designed to reduce voltage from primary to secondary called step-down transformer.
Transformer turns ratio k=(n2/n1)=(v2/v1)=20.
v1=12 (voltage at primary)
therfore voltage at secondary (v2)=(k*v1)=(20*12)=240v.