Question 413: AC fundamentals

Question

A step down transformer has turns ratio $$20: 1$$. If $$8 \mathrm{~V}$$ is applied across $$0.4 \mathrm{~ohm}$$ secondary then the primary current will be

Accepted Answer

To find the primary current in the transformer, we can follow a stepwise method that involves understanding the relationship between the transformer's turn ratio and the currents on the primary and secondary sides, as well as using Ohm's law for finding the currents.
The turns ratio of a transformer is given as $$N_P : N_S = 20 : 1$$, where $$N_P$$ is the number of turns on the primary coil, and $$N_S$$ is the number of turns on the secondary coil. The voltage applied across the secondary is given as $$8 \, 	ext{V}$$, with the resistance across the secondary being $$0.4 \, \Omega$$.
First, let's find the secondary current using Ohm's Law, $$V = IR$$. Thus, the secondary current can be calculated as follows:
$$I_S = \frac{V_S}{R_S}$$
Substituting the given values,
$$I_S = \frac{8 \, 	ext{V}}{0.4 \, \Omega} = 20 \, 	ext{A}$$
The transformation ratio relating primary and secondary currents and the turns ratio is given by:
$$\frac{N_P}{N_S} = \frac{I_S}{I_P}$$
Where $$I_P$$ is the primary current. We can rearrange this equation to solve for $$I_P$$:
$$I_P = \frac{N_S}{N_P} 	imes I_S$$
Given the turns ratio $$20:1$$, we substitute the values:
$$I_P = \frac{1}{20} 	imes 20 \, 	ext{A} = 1 \, 	ext{A}$$
Therefore, the primary current in the transformer is $$1 \, 	ext{A}$$.
So, the correct option is:
Option B: 1 A

Answer

2 A

Answer

1 A

Answer

0.5 A

Answer

4 A

AC fundamentals

A step down transformer has turns ratio $20: 1. If 8 \mathrm{~V} is applied across 0.4 \mathrm{~ohm}$ secondary then the primary current will be

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