# A voltage step-up transformer with a 1 : 5 turns ratio has 220 V across 2200 ohms in the secondary. Calculate the value of primary current.

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A voltage step-up transformer with a 1 : 5 turns ratio has 220 V across 2200 ohms in the secondary. Calculate the value of primary current.
1. 0.1 A
2. 0.5 A
3. 1.0 A
4. 220 mA

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Correct Answer - Option 2 : 0.5 A

Concept-

Transformer:

• An electrical device that is used to transfer electrical energy from one electrical circuit to another is called a transformer.

There are two types of transformer:

1. Step-up transformer:

• The transformer which increases the potential is called a step-up transformer.
• The number of turns in the secondary coil is more than that in the primary coil.

2. Step-down transformer:

• The transformer which decreases the potential is called a step-down transformer.
• The number of turns in the secondary coil is less than that in the primary coil

In a transformer:

$\frac{{{I_S}}}{{{I_P}}} = \frac{{{N_P}}}{{{N_S}}}$

Where IS is current in the secondary coil, IP is current in the primary coil, NS is the number of turns in the secondary coil and Np is the number of turns in the primary coil.

Explanation

Given that:

Load current = Secondary current (IS) = 220/2200 = 0.1 A

Ratio of primary to secondary winding (NP/NS) = 1/5

$\frac{{{I_S}}}{{{I_P}}} = \frac{{{N_P}}}{{{N_S}}}$

$\frac{0.1}{{{I_P}}} = \frac{{{N_P}}}{{{N_S}}} = \frac{1}{{5}}$

Primary current (IP) = 0.5 A