A step down transformer increases the input current 4A to 24A at the secondary. If the number of turns in primary coil is 330, the number of turns in secondary coil is:
(A) 60
(B) 50
(C) 65
(D) 45
(E) 55

Hint: In the step-up transformer the voltage increases from the primary coil to the secondary coil.

Formula used:
\[\dfrac{{{V_P}}}{{{V_S}}} = \dfrac{{{I_S}}}{{{I_P}}} = \dfrac{{{N_P}}}{{{N_S}}}\]
Where, ${N_P}$is number of turns in primary, ${N_S}$is number of turns in secondary coil, ${V_P}$ is voltage in primary coil, ${V_S}$ is voltage in secondary coil, ${I_P}$ is current in primary coil and ${I_S}$ is current in secondary coil.

Complete step-by-step answer:
Following is given in the question.
${I_P} = 4A,{I_S} = 24A,{N_P} = 330$
We have to find the number of turns in the secondary coil (${N_S}$).
Now, let us use the formula \[\dfrac{{{I_S}}}{{{I_P}}} = \dfrac{{{N_P}}}{{{N_S}}}\]to calculate${N_S}$.
We can now substitute the values in the formula.
\[\dfrac{{{I_S}}}{{{I_P}}} = \dfrac{{{N_P}}}{{{N_S}}}\]
\[\dfrac{{24}}{4} = \dfrac{{330}}{{{N_S}}}\]
After simplifying we get the following.
${N_S} = \dfrac{{4 \times 330}}{{24}} = 55$
The number of turns in the secondary coil is 55
Hence, option (E) 55 is correct.

Additional information:
An electrical device is required to transform the current from one circuit to another. The electrical device is known as a transformer.
There are two types of transformer (1) step-up transformer (2) step-down transformer.
More number of turns are present in the primary than the secondary. It converts low voltage high current power into high voltage low current power.
The step-up transformer increases the output voltage and the step-down transformer decreases the output voltage.
In the step-up transformer, the voltage binding is high. In step down transformers, the voltage binding is low.
The step-down transformer decreases the voltage from the primary to the secondary coil. It converts high voltage, low current power into low voltage high current power.
Note:
The application of the step-up transformer in India is more. In India usually, the power is generated at 11kv. For more economical reasons the power is transmitted in higher voltages and hence the step-up transformer used.