Question

The number of turns in the primary coil of a transformer is 200 and the number turns in the secondary coil is 10 If 240 volt a.c is applied to the primary. The output from secondary will be:
A) 48 V
B) 24 V
C) 12 V
D) 6 V

Answer 1

Hint:Transformers are commonly used to increase or decrease the supply voltage without a change in the frequency of AC between circuits. The output from secondary will be given by${V_2}$ =$\dfrac{{\left( {{V_1}} \right)\left( {{N_2}} \right)}}{{{N_1}}}$
Where, ${N_1}$ =number of primary winding turns, ${N_2}$ =number of secondary winding turns, ${V_1}$=primary side voltage and ${V_2}$ =secondary side voltage

Step by step solution:

Step 1:
Before solving the question let us study about what is transformer and how it works
A transformer is a device used in the power transmission of electric energy. 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 basic principles of electromagnetic induction and mutual induction.
There are usually two coils, primary coil and secondary coil on the transformer core. The core laminations are joined in the form of strips. The two coils have high mutual inductance. When an alternating current pass through the primary coil, forms a varying magnetic flux as per faraday’s law of electromagnetic induction and this change in magnetic flux induces an emf (electromotive force) in the secondary coil which is linked to the core having a primary coil. This is mutual induction

Step 2:
The equation of transformer is given by $\dfrac{{{N_1}}}{{{V_1}}} = \dfrac{{{N_2}}}{{{V_2}}}$ ……. (1) Where,
${N_1}$ =number of primary winding turns
In question we are given ${N_1}$ =200
${N_2}$ =number of secondary winding turns
In question we are given ${N_2}$ =10
${V_1}$=primary side voltage
In question we are given ${V_1}$=240V
 ${V_2}$ =secondary side voltage
We need to find secondary side voltage
Putting in equation (1)
${V_2}$ =$\dfrac{{\left( {{V_1}} \right)\left( {{N_2}} \right)}}{{{N_1}}}$ Substituting the value we get ${V_2}$ =$\dfrac{{240 \times 10}}{{200}}$
On further solving it we will get ${V_2}$ =12 V

Hence option C is the correct answer.

Note:
There are many other questions based on the formula of the transformer. Just remember the basic formula of $\dfrac{{{N_1}}}{{{V_1}}} = \dfrac{{{N_2}}}{{{V_2}}}$ and then we can find any value by the help of other three given values.