1. An American traveler in a foreign country carries a transformer to convert th

Question

1. An American traveler in a foreign country carries a transformer to convert that country's standard 177 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 motor operating on 236 V electricity has a 164 V back emf at operating speed and draws a 12.2 A current. What is it's resistance?

3. A motor operating on 224 V electricity has a 160 V back emf at operating speed and draws a 12.9 A current. What current does it draw when it is first started?

4. At what angular velocity in rpm will the peak voltage of a generator be 470 V, if its 376-turn, 8.77 cm diameter coil rotates in a 0.212 T field?

Explanation / Answer

1) Turn ratio

N2/N1 = V2/V1 = 120/177 = 0.677

2) V = E - IR

164 = 236 - 12.2*R

R = 5.9 ohm

3) V = E - IR

160 = 224 - 12.9*R

R = 4.96 ohm

V = IR

160 = 4.96*I

I = 32.25 A

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