Alternating Current - Result Question 40

42. A step-up transformer operates on a $230 V$ line and supplies a load of 2 ampere. The ratio of the primary and secondary windings is $1: 25$. The current in the primary is

[1998]

(a) $25 A$

(b) $50 A$

(c) $15 A$

(d) $12.5 A$

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Answer:

Correct Answer: 42. (b)

Solution:

(b) $\frac{N_p}{N_s}=\frac{E_p}{E_s}=\frac{1}{25}$

$\therefore E_s=25 E_p$

But $E_s I_s=E_p I_p$

$25 E_p \times 2=E_p \times I_p \Rightarrow I_p=50 A$

If $n_p$ is number of turns in primary coil and $n_s$ is number of turns in secondary coil, then

$\frac{E_s}{E_p}=\frac{I_p}{I_s}=\frac{n_s}{n_p}=k$

Here, $I_p=$ current in primary

$k=$ Transformation ratio

$I_s=$ current is secondary

For a step up transformer, $k>1$

For step down transformer, $k<1$