Question

An American traveler in Kenya carries a transformer to convert Kenya's standard 240 V to 120 V so that she can use some small appliances on her trip. (a) What is the ratio of turns in the primary and secondary coils of her transformer? Np Ns = (b) What is the ratio of input to output current? Iin Iout = (c) How could a Kenyan traveling in the United States use this same transformer to power her 240 V appliances from 120 V?

Answer 1

a)
`N_(p)`/
`N_(s)` = 2

b)
`I_(in)`/
`I_(out)` = 0.5

c) A Kenyan travelling in the united states will now use the output terminal of the transformer in Kenya as the input terminal in the United States, to step up the voltage from 120 V to 240 V for his devices

Step-by-step explanation:

Kenya's standard voltage
`V_(p)` = 240 V

America's standard voltage
`V_(s)` = 120

using the transformer relationship

`V_(p)`/
`V_(s)` =
`N_(p)`/
`N_(s)`

substituting values, we have

240/120 =
`N_(p)`/
`N_(s)`

`N_(p)`/
`N_(s)` = 2

b) The power input must be equal to the power output

`I_(in)`
`V_(in)` =
`I_(out)`
`V_(out)`

where
`I_(in)` = input current

`V_(in)` = input voltage = 240 V

`I_(out)` = output current

`V_(out)` = output voltage = 120 V

Transposing the above equation, we get

`I_(in)`/
`I_(out)` =
`V_(out)`/
`V_(in)`

`I_(in)`/
`I_(out)` = 120/240 = 0.5

c) A Kenyan travelling in the united states will now use the output terminal of the transformer in Kenya as the input terminal in the United States, to step up the voltage from 120 V to 240 V for his devices.