(1) A transformer is designed to step 230 V European power down to 120 V needed
ID: 2011612 • Letter: #
Question
(1) A transformer is designed to step 230 V European power down to 120 V needed to operate North American devices. (a) If the primary has 800 turns, how many should the secondary have? (b) If the primary current is 5.0 A, what is the secondary current?(2) A coil has a resistance of 60 ohms and an impedance of 100 ohms. Its reactance, in ohms, is
(Hint: understand the definition of Reactance and Impedance):
(A) 60 Ohms
(B) 80 Ohms
(C) 117 Ohms
(D) 160 Ohms
(E) 40 Ohms
(3) The Sun is about 1.5 x10^11 m away. The time for light to travel this distance is about
A. 4.5x10^18s
B. 8 s
C. 8 min
D. 8 hr
E. 8 yr
Explanation / Answer
(1) (a) for a transformer we know that V1/V2=N1/N2 so 230/120=800/N2 N2=417.38=418 turns (b) I1/I2=N2/N1 so 5/i2=418/800 i2=9.569 amps (2) X=sqrt(Z^2-R^2) X=sqrt(100^2-60^2)=80 ohms (3) time=dictance/velocity of light=1.5*10^11/3*10^8=500 sec=8.33 min
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