Question

A step up transformer is connected to an ac mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer, is

• A. 8 mA
• B. 4 mA
• C. 0.4 A
• D. 4 A

Answer 1

The Correct Option is A

Principle: For an ideal transformer, ignoring power loss:

$$ P_{\text{primary}} = P_{\text{secondary}} $$ 

Where Power $P = VI$

Given:

$$ V_p = 220 \, \text{V} \quad \text{(Primary voltage)} $$ $$ V_s = 11000 \, \text{V} \quad \text{(Secondary voltage)} $$ $$ P = 88 \, \text{W} \quad \text{(Power)} $$ $$ I_s = ? \quad \text{(Secondary current)} $$

Solution:

Using $P_s = V_s I_s$:

$$ 88 = 11000 \times I_s $$

Solving for $I_s$:

$$ I_s = \frac{88}{11000} = \frac{88}{11 \times 10^3} $$

$$ I_s = 8 \times 10^{-3} \, \text{A} $$

Converting to milliamps:

$$ I_s = 8 \, \text{mA} $$