Question

A certain transformer has a turn ratio of 1 and a 0.85 coefficient of coupling. When 2 V ac is applied to the primary, the secondary voltage is
A) 1.7V
B) 0.85V
C) 1V
D) 0V

Answer 1

Hint: The question based on the transformer and its turn ratio. The turn ratio of the transformer is $\dfrac{{{N_s}}}{{{N_p}}}$ =1. The output voltage in secondary coil be ${V_s}$ =$\eta \dfrac{{{N_s}}}{{{N_p}}}{V_p}$ where, ${V_s}$ is secondary coil, $\eta $ is coefficient of coupling and voltage in primary coil as ${V_p}$.

Complete step by step answer:
Commonly used transformer type, depending upon voltage they are classified as:
Step-up Transformer: They are used between the power generator and the power grid. The secondary output voltage is higher than the input voltage.
Step-down Transformer: These transformers are used to convert high voltage primary supply to low voltage secondary output.
A transformer is a device used in the power transmission of electric energy and turn ratio of the transformer $\dfrac{{{N_s}}}{{{N_p}}}$ =1
The transmission current is AC. It is commonly used to increase or decrease the supply voltage without a change in the frequency of AC between circuits. The transformer works on the basic principles of electromagnetic induction and mutual induction.

Now coming to the question,
We are given: coefficient of coupling $\eta $ =0.85
Let the input voltage in the primary coil denoted as ${V_p}$, and ${V_p}$=2V
Turn ratio of the transformer $\dfrac{{{N_s}}}{{{N_p}}}$ =1
Thus output voltage in secondary coil be ${V_s}$ =$\eta \dfrac{{{N_s}}}{{{N_p}}}{V_p}$
Putting all the values we will get the output voltage,
$\Rightarrow {V_s} =0.85 \times 1 \times 2$
On simplification,
$\Rightarrow {V_s} = 1.7$ Volt

$\therefore $ The secondary voltage is 1.7 volt. Option A is correct.

Additional information:
Application of transformers:
- The transformer transmits electrical energy through wires over long distances.
- Transformers with multiple secondaries are used in radio and TV receivers which require several different voltages.
- Transformers are used as voltage regulators.

Note:
A transformer consists of two electrically isolated coils and operates on Faraday's principle of mutual induction, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.