Calculation of Efficiency

To calculate the efficiency of a transformer, we need to use the formula:

Efficiency = (Output Power/Input Power) x 100%

Here, the input power is the power drawn by the primary and the output power is the power delivered to the secondary.

Let's calculate the input power first:

Input Power = 220 V x 5 A = 1100 W

Now, let's calculate the output power:

Output Power = 11 V x 90 A = 990 W

So, the efficiency of the transformer is:

Efficiency = (990/1100) x 100% = 90%

So, the correct answer is option D (90%).

Explanation

A transformer is an electrical device that is used to transfer electrical energy from one circuit to another by means of electromagnetic induction. It consists of two coils, the primary and the secondary, which are wound around a common core. When an alternating current is passed through the primary coil, it creates a magnetic field which induces a voltage in the secondary coil. The voltage induced in the secondary coil depends on the ratio of the number of turns in the primary coil to the number of turns in the secondary coil.

In this question, the transformer is used to reduce the voltage from 220 V to 11 V. The primary draws a current of 5 A, which means that the input power is 1100 W. The secondary draws a current of 90 A, which means that the output power is 990 W. The efficiency of the transformer is calculated using the formula mentioned above, which gives us an efficiency of 90%. This means that 90% of the input power is delivered to the output, while the remaining 10% is lost as heat due to various losses in the transformer.

Efficiency =output power / input power *100
=IV /I'V' *100
=(11*90/220*5) *100
= 990/1100 *100
= 90%
(power =V*I)