Question

A transformer for charging a power tool steps the line voltage down to 2.9 V. The output current of this transformer is 240 mA. If the transformer is ideal (100% efficient), what is the input current

Answer 1

The input current is 5.8 mA

Step-by-step explanation:

Given;

output voltage of the transformer, V₀ = 2.9 V

output current of the transformer, I₀ = 240 mA = 0.24 A

efficiency of the transformer, E = 100%

the electrical outlet of most homes is 120 V = input voltage

The input power is calculated as follows;

`E = (0utput \ power)/(1nput \ power) * \ 100\%\\\\1nput \ power = (0utput \ power)/(E) * \ 100\%\\\\E = 100\%\\\\1nput \ power = 0utput \ power\\\\1nput \ power = V_0 I_0 \\\\1nput \ power = 2.9 \ * 0.24\\\\1nput \ power = 0.696 \ W`

input power = IV

where;

V is input voltage

I is input current

I x 120 = 0.696

I = 0.696 / 120

I = 5.8 x 10⁻³ A

I = 5.8 mA