Question

1. An American traveler in a foreign country carries a transformer to convert that country's standard 175 V to 120 V so that she can use some small appliances on her trip. What is the ratio of turns in the primary and secondary coils of her transformer?

2. A device is turned on and 3.34 A flows through it 0.161 ms later. What is the self-inductance of the device if an induced 177 V emf opposes this? Give your answer in millihenries.

Answer 1

here,

the voltage in primary , Vp = 175 V

the voltage in secondary , Vs = 120 V

for ideal transformer

the ratio of turns in the primary and secondary coils of her transformer , R = Np /Ns = Vp / Vs

R = 175 /120 = 1.46

2)

change in current , dI = 3.34 A

the time taken , dt = 0.161 ms = 1.61 * 10^-4 s

the emf , V = 177 V

let the self-inductance be L

V = L * dI /dt

177 = L * 3.34 /(1.61 * 10^-4)

solving for L

L = 8.53 * 10^-3 H = 8.53 mH

the inductance is 8.53 mH