Question

A step down transformer changes the high input voltage used in our houses $\left(120V\right)$ into the low voltage used to charge an electric razor $\left(24V\right)$. What must be the ratio of the turns of wire from the primary side of the transformer to the secondary side?

• A. $1:5$
• B. $2:7$
• C. $1:8$
• D. $2:9$
• E. $1:10$

Answer 1

The correct option is A $1:5$

We know that transformation ratio is given by ,

$N_s/N_p=V_{out}/V_{in}$

given - $V_{in}=120V,V_{out}=24V$

therefore , $N_s/N_p=120/24$

or $N_p/N_s=24/120=1/5$