Question

When the turns ratio of a step-up transformer is $20$ and the primary ac voltage is $12V$, the secondary voltage is

• A. $12V$
  
• B. $120V$
  
• C. $240V$
  
• D. $2,400V$
  

Answer 1

The correct option is C $240V$

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.

For step-up transformer, turns ratio $n=\frac{V_s}{V_p}$ or $20=V_s/12$ or $V_s=240V$

For step-down transformer, turns ratio $n=\frac{V_p}{V_s}$ or $20=12/V_s$ or $V_s=0.6V$