Chapter 37, Problem 52A

An electric doorbell requires 12 volts to operate correctly. A transformer nicely allows it to be powered from a 120-volt outlet. If the primary has 500 turns, show that the secondary should have 50 turns.

To determine

To show: there are $50turns$ in the secondary coil

Answer to Problem 52A

The number of turns on secondary coil is $50turns$

Explanation of Solution

Given:

Voltage of electric doorbell $\left(V_2\right)=12V$

Transformer voltage $\left(V_1\right)=120V$

Number of turns on primary coil $\left(N_1\right)=500$

Number of turns on secondary coil $\left(N_2\right)=50$

Formula used:

  $\frac{V_1}{V_2}=\frac{N_1}{N_2}$.

Calculation:

The relation between voltage and number on turns on primary and secondary winding is,

  $\frac{V_1}{V_2}=\frac{N_1}{N_2}$

The equation becomes,

  $\begin{array}{l}{N}_2=N_1\frac{V_2}{V_1}\\ N_2=500\times \frac{12}{120}\\ =50turns\end{array}$

The number of turns required on the secondary winding is $50turns$

Conclusion:  The number of turns on the secondary winding is $50turns$